At nearly every step in the career of Speaker Nancy Pelosi (D-Calif.), Rep. John Murtha (D-Pa.) has been by her side, lending public support and private muscle to her ascent.

But now that she has reached the top of the House — even as Pelosi allies say she remains steadfastly loyal to Murtha — the Pennsylvanian’s increasingly controversial behavior on a variety of fronts has made his longtime friend’s first months on the job a lot more difficult.

In recent weeks, Murtha has drawn attention on a national stage, not only for his opposition to the Iraq War and a proposal to curtail the White House’s ability to conduct that fight, but also for his aggressive — possibly threatening — defense of the Speaker’s request for a military plane to travel to her district. And those high-profile incidents came less than two months after Murtha was trounced in a race for Majority Leader despite Pelosi’s public endorsement.

While he holds no official place on the Democratic leadership roster aside from his post as an Appropriations cardinal, overseeing Defense spending, Murtha is among Pelosi’s closest advisers; some Democrats say his influence with her is rivaled only by the Speaker’s fellow Californian, Rep. George Miller (D).

For his part, the 18-term lawmaker largely brushes aside inquiries on the subject, stating of his role in the Caucus: “I don’t know that I have a role in the leadership. I just do what’s right.”

While Murtha may downplay his position, however, his profile remains high, effectively magnifying his every action. But unlike his elected brethren in leadership, constrained in part by the fact that they speak for the entire Caucus, Murtha lacks any particular limitations on his decisions.

“He’s not beholden to any structure beyond the chairmanship,” acknowledged one Democratic lawmaker, who requested anonymity. “It’s a double-edged sword not having those constraints.”

That potential danger showed most recently, when Murtha — anointed by Pelosi as the Democrats’ lead voice on Iraq late last year — ruffled feathers among his colleagues for announcing his proposal to curtail the Iraq War through the use of Congressional purse strings. That proposal called for the enforcement of rules governing how much time troops must have between missions as well as training requirements, effectively reducing the number of available military units.

It wasn’t only what the Pennsylvania lawmaker said, however, that gained attention, but his decision to publicize his plans on an anti-war Web site in the midst of the House debate on a resolution opposing President Bush’s plans to send more than 21,500 additional troops to Iraq.

“Our problems [on the Iraq debate] started when Jack Murtha opened his mouth,” asserted one Democratic operative, who asked not to be named.

By making his announcement before the House could complete debate on that resolution, critics argue, Murtha effectively shifted attention away from the White House and back to the question of Democratic support for the military.

“In his pursuit of headlines he’s taken the war from 1600 Pennsylvania Ave. to the Democrats’ doorstep,” said the operative.

But even as Democrats move to shed Murtha’s initial proposal — moving toward a plan that would instead force President Bush to sign waivers any time rules dictating rest periods and training levels for troops are set aside, rather than blocking the deployment of military personnel and calling for renewed focus on Afghanistan — Pelosi insists that the Pennsylvania lawmaker is not a liability to the party.

“He’s a tremendous asset, 37 years in the Marines as active duty and reserve,” Pelosi said during a Tuesday appearance on “Larry King Live.” “In fact, a poll that came out today, a survey of the American people had overwhelming support for what Mr. Murtha is saying.”

According to some Democratic critics, many of whom asked not be named citing the sensitive nature of the subject, that assertion rang hollow Wednesday.

“There are many who believe [the Speaker] is quite frustrated with the approach and style he has taken,” said one former House Democratic staffer, who spoke on the condition of anonymity.

Nonetheless, because Murtha is among the Speaker’s closest allies, few Democrats said they expect her to demand any kind of change. “Whether she reins him in or not is a big unknown,” the former staffer added.

But Rep. Mike Capuano (D-Mass.), a close ally of Murtha, defended the Pennsylvania lawmaker’s recent actions on Iraq, including his decision to publicize his plan via an anti-war Web site, rather than in a formal setting or one-on-one with lawmakers.

“I’m happier with the way it’s going right now,” Capuano said, noting that he did not agree with all aspects of Murtha’s initial plan. “It’s a cleaner vote for me.”

While Murtha’s proposal also has drawn criticism from some corners of the Democratic Caucus — members of the fiscally conservative Blue Dog Coalition have disparaged the plan — Capuano asserted it does not impact the senior lawmaker’s ability to act as the front-man on Iraq for the majority.

“No one person can represent every interest of everybody … but that doesn’t mean he’s not the face of the Caucus,” Capuano said.

A Democratic strategist who asked not to be named argued the ongoing debate over how to frame the supplemental spending bill is more the result of infighting between factions of the Caucus over how to craft the bill, and has little to do with how Murtha elected to announce his proposal.

“That’s a problem that transcends him,” the strategist said.

Capuano asserted that Murtha maintains his stature in the Caucus.

“A lot of people come to him for counsel … he’s a Member’s Member,” Capuano said, noting the line of lawmakers waiting to speak with Murtha on the House floor during a recent vote.

Still, other colleagues close to Murtha, who spoke on the condition of anonymity, said there has been a notable change in the lawmaker’s demeanor as the Iraq War debate rolls forward.

One lawmaker said Murtha has taken an almost obsessive focus on the troops in Iraq and Afghanistan, but disputed criticisms that Murtha’s Iraq strategy could hurt troop’s in harm’s way. “There is no way I can believe that Jack Murtha would do anything to hurt troops fighting in the field,” the lawmaker said.

However, multiple sources said Murtha has been increasingly volatile and impatient on the Appropriations Committee during hearings about to the war.

Multiple sources recounted a Feb. 9 hearing on Army funding with Army Chief of Staff Peter Schoomaker and Army Secretary Francis Harvey during which Murtha snapped at ranking member Jerry Lewis (R-Calif.) both during and after the hearing for comments Lewis had made during the hearing.

“He just went up to him afterward and started yelling at Jerry,” said a source, “It was almost out of line to do it so publicly.”

Another lawmaker noted that even aides on the powerful Appropriations panel have taken note of Murtha’s increasingly aggressive approach to the war. “Everyone’s sort of walking on egg shells around him,” the lawmaker said.

In the hallway outside his Rayburn Building office Wednesday, Murtha maintained a more friendly demeanor, shaking the hands of two visitors who stopped to praise the lawmaker’s attention to the war

“There’s no question many people were elected [in November] because I was speaking for people who want the troops redeployed,” Murtha said inside his office, referring to his decision to publicly oppose the war in 2005, and the 2006 election cycle that returned Democrats to the majority.

“I have helped change the direction of the country,” Murtha added, citing among his apparent influences the Bush administration’s announcement Wednesday that the United States will participate in an Iraqi government initiated regional conference along with Iran and Syria to discuss the country’s future. The Pennsylvanian said he expects that decision is among the significant changes Bush will be required to make in coming months, adding: “In the end he’s going to redeploy.

But when asked about pending negotiations on the supplemental bill, Murtha defers credit, stating: “In the end it’s not going to be my bill and what I said. … The public is what really controls this.”

Revisiting the skirmish that ensued in January over whether the Speaker would receive a military aircraft for travel to and from Washington, D.C., Murtha similarly played down his actions, even as he emphatically defended Pelosi’s request — to match the privilege extended to her predecessor, then-Speaker Dennis Hastert (R-Ill.) — noting that he has sought the same privilege for each of the Democratic Speakers he has served under.

“All I did was call the Air Force and say let’s take care of this,” Murtha said.

While one Democratic strategist praised Murtha’s response Wednesday as “perfectly appropriate,” Republicans capitalized on the incident, characterizing the request as “Pelosi One” and an unnecessary perk. The GOP also seized specifically on Murtha’s role, saying that he had threatened the Pentagon’s budget over the issue.

One Democratic lawmaker, who asked not to be identified, suggested the true test for Murtha’s influence will come as the House takes up the $100 billion supplemental spending bill, first in committee next week and on the House floor in mid-March. “This is a very defining moment for Jack,” the Member said.

Another Democratic source asserted of Murtha: “He has become not only the leader [on Iraq] as defined by the Democrats, but the Republicans. … [Democratic leaders] have to patch [the supplemental] together without embarrassing him,” the source added.

Whether that outcome affects Murtha’s public behavior remains to be seen.

“He got bitten by the national media — he likes being out front, in the forefront,” said a Democratic lawmaker, noting Murtha’s exposure since his announcing his opposition to the war, as well as his subsequent bid for the Majority Leader’s officer.

While Pelosi backed Murtha for that post, among the most significant moves the then-Speaker-to-be made in the wake of November’s elections, he ultimately lost the race badly, falling 149-86 to now Majority Leader Steny Hoyer (D-Md.)

“The loss of the majority leader’s race was stunning and it impacted him very strongly,” the Democratic lawmaker added.

But while that failed bid may have tarnished Pelosi’s initial days, that loss at least let Murtha retain his ability to serve as an attack dog for the Speaker without the party leadership being specifically tied to his statements or promises.

“You sometimes want people out on point who you can … disavow,” said a Democratic strategist.

Susan Davis contributed to this report.