Senate Majority Whip Dick Durbin (Ill.) is used to corralling votes for his Conference, but in recent days the No. 2 Democratic leader has tapped into that experience to try to persuade Senators to publicly back his home-state presidential aspirant, Sen. Barack Obama, over fellow Sen. Hillary Rodham Clinton (N.Y.).

Durbin has long been Obama’s biggest and most vocal Senate backer, but in the wake of Obama’s resounding victory at the Iowa caucus, the Illinois Democrat has been burning up the Senate phone lines to try to grow his candidate’s bandwagon. Up until late December, Durbin was the lone Obama endorsement in the Senate.

Several Democrats familiar with Durbin’s whip operation for Obama say the veteran lawmaker has seemingly left no Senator to chance — having placed in some cases several calls to uncommitted Members to make a case for Obama’s surging candidacy. Atop the target list appear to be moderate- and rural-state Senators and women — for whom Obama is competing heavily for support against Clinton.

“Durbin is working it hard, definitely,” said one senior Democratic Senate aide whose boss has received an appeal. “Calls are being made.”

Another well-placed Senate Democratic aide agreed, saying: “He’s a player in this. He’s certainly working on behalf of Obama to get members on board — there’s no question about that.”

In an interview last week, Durbin acknowledged he’s doing all he can to advance Obama’s campaign, including encouraging his fellow Democratic Senators to jump aboard. But Durbin downplayed using any of the traditional Whip tactics to try to cajole lawmakers to publicly ally with his presidential pick.

“Any of my colleagues I’m talking to, there’s no pressure involved at all,” Durbin said. “I want them to do what’s right for them as Senators.”

Durbin said it is rare for a Whip to engage in “forcing [Senators] to do what they otherwise wouldn’t want to do” when it comes to Senate votes, and it “certainly is not the case” when it comes to mobilizing Senate support for Obama.

Beyond making a personal appeal on the merits, Durbin could offer Senators little in exchange for a public endorsement beyond pledging to help them raise money or perhaps offering to line up a future Obama visit to the lawmaker’s home state.

Whether Durbin’s involvement has led to Obama’s recent uptick in Congressional endorsements remains unclear, but most Democrats agree that it hasn’t hurt. It also hasn’t hurt that Durbin has spent innumerable hours traveling with or on behalf of the presidential frontrunner, most recently in Iowa and New Hampshire.

As one Democratic strategist who is unaffiliated with either campaign said: “If I had to pick someone I’d want doing this job for me, I’d want Durbin.”

Obama has won a number of endorsements in recent days, including the party’s 2004 presidential nominee, Sen. John Kerry (Mass.), and moderate Sen. Tim Johnson (S.D.), who faces re-election this year in a Midwestern swing state. Sources say a number of other Senators are on Obama’s radar and have been heavily courted, including female Sens. Claire McCaskill (Mo.) and Patty Murray (Wash.) and Sen. Patrick Leahy (Vt.).

Rural Senators also have been targeted, including Montana Sens. Max Baucus and Jon Tester and North Dakota Sen. Byron Dorgan. Dorgan has said he won’t endorse before a nominee is declared, but his home-state colleague Sen. Kent Conrad became the second Senator to sign onto the Obama camp just two weeks ago.

Unlike Obama, who only recently experienced an increase in support from fellow Senators, Clinton has enjoyed strong backing from her colleagues for many months. The former first lady has at least 10 Senators in her corner, with her greatest allegiance coming from the chamber’s female lawmakers.

As the establishment candidate, many believe Clinton has less riding on whether her colleagues agree she’s the best fit to be the next president. Clinton doesn’t need to prove she has the experience or the wherewithal to step into the Oval Office upon assuming the presidency.

Obama, however, must demonstrate that beyond inspiring voters he is also prepared for the duty. Capturing the support of his colleagues would show that even the most seasoned political hands view the first-term Senator as fit to serve as the commander in chief.

“Endorsements generally mean very little, but they are heightened in this instance because Obama is countering the idea that he’s not ready to be president,” the Democratic strategist said. “The more of his colleagues endorsing him shows he’s ready.”

Still, virtually every House and Senate Member may be worth getting since each enjoys “superdelegate” status and has a voting role at the party nominating conventions later this year. The superdelegate position is largely ceremonial, but in a highly unusual political year, there is a remote possibility that those delegate votes could help determine the Democratic nominee.

Indeed, the race is exceedingly tight between Obama and Clinton, and convention delegates or not, both candidates need all the help they can get from their endorsements whether it’s at the grass roots or simply to show new momentum for their campaigns.

“This is a very close race in both parties, and in a close race you’ve got to do everything,” said Steve Elmendorf, president of Elmendorf Strategies and a declared Clinton backer.

At least a handful of prominent Senators’ endorsements are of special interest to both Clinton and Obama, including the one-time 2008 hopefuls Sens. Joseph Biden (Del.) and Chris Dodd (Conn.), as well as liberal stalwart Sen. Edward Kennedy (Mass.) and possibly the remaining female Senators who are uncommitted, such as Murray and Sen. Barbara Boxer (Calif.).

Most Democrats expect that any Member who has yet to endorse and hopes to curry influence with the prospective nominee will want to sign up before the nominating process is over. It’s widely believed that Clinton or Obama will emerge as their party’s choice for president by Feb. 5, the Super Tuesday primary day in which 22 states will hold contests.

Sen. Bob Menendez (N.J.), who has been backing Clinton for months, said Friday that Senators understand that if they are going to get behind a candidate and they “want their endorsement to mean something, it seems to me that the next 25 days or so is the time that it will mean something.”

Menendez aligned with Clinton early on because of the two Senators’ close personal ties, long-standing working relationship and shared home-state interests. Like Durbin has for Obama, Menendez has served as Clinton’s surrogate, helped her in her debate preparations and advised his New York colleague on numerous issues relating to the Latino community.

Asked about Clinton’s endorsement tally to date, Menendez said: “I think it’s pretty exceptional … it speaks to the breadth and scope of her experience with people in the House and Senate.”

Certainly, Durbin’s role in Obama’s campaign is not uncommon this political season — especially since three Senators are enjoying the label of frontrunner in their respective party contests. As Clinton and Obama duke it out on the Democratic side, Sen. John McCain (Ariz.) has risen from the political ashes to become a leading contender in the still-crowded Republican field.

McCain has long put a premium on having Senate endorsements, hoping to convince the Republican establishment that he’s not the outsider candidate he was in 2000 and has credibility among some of the chamber’s most conservative members. Sen. Lindsey Graham (S.C.) has spent hundreds of hours as McCain’s leading surrogate and trying to grow his support in the key Southern state.

Last week, Graham teamed up with Sens. Jon Kyl (Ariz.) and former Sen. Trent Lott (Miss.) to campaign across his home state for McCain. Similarly, former presidential aspirant and now McCain backer Sen. Sam Brownback (Kan.) also hit the trail there for his colleague.

Sen. John Thune (R-S.D.), fresh off a New Hampshire trip for McCain, said at the very least Senate support is “a measure of the depth of commitment that a lot of people have for McCain.”

“People who know him best are out on the ground for him,” Thune said.