If former Sen. John Breaux (D-La.) jumps into his home state’s gubernatorial contest, the move would not simply upend the race. It also could have a significant impact on the bottom line of one of Washington’s biggest lobbying players, Patton Boggs, the firm he joined at the beginning of 2005.

Breaux has said he will enter the race if the Louisiana attorney general gives him the OK, even though the former Senator does not currently reside in the Pelican State. If he runs, he is expected to either resign or take a leave of absence from Patton Boggs.

While the firm officially remains tight-lipped about what that would mean, several insiders and lobbyists at rival firms say that losing Breaux, who by all accounts has been a boost to the firm’s client development, would hurt.

“I think it’s a loss for the firm because he’s so high-profile and because he is so adept and well-liked by both sides of the aisle,” said Ivan Adler, a lobbyist headhunter at the McCormick Group.

Current and former Breaux colleagues say the former Senator has helped Patton Boggs lobbyists attract new business by participating in numerous meetings to pitch potential clients. Breaux is perhaps second only to the firm’s other big-name rainmaker, Tom Boggs Jr.

“He’s been huge there,” said one lobbyist familiar with Patton Boggs. “He has been seen as the future of the firm.”

Breaux’s registered clients include the government of Peru, a $50,000-a-month client; Verizon; Wal-Mart Stores Inc.; and the Louisiana Department of Economic Development, among others.

“Having him on the team vastly increased the amount of the client retainer,” said another lobbyist knowledgeable of Patton Boggs, who would not be quoted by name. “There is no question that there are going to be clients that will revisit their contracts after he leaves.”

Because much of Breaux’s work at Patton Boggs includes helping to bring in new business and giving big-picture strategic advice, it’s impossible to tell from public disclosures how much Breaux is worth to the firm that reportedly pays him an annual salary of $2 million. But several sources said that his book of business is at least double that $2 million, and some sources said that people inside Patton Boggs privately have said Breaux is responsible for as much as $12 million in revenue.

In 2004, the year before Breaux joined Patton Boggs, the firm reported $31 million in lobbying revenue. In 2005, that figure jumped to $36 million. Last year, Patton Boggs’ numbers dipped to $34 million. A spokesman for Patton Boggs said the firm did not have a comment by press time.

“He’s a powerhouse, there’s no question about it,” said Ron Christie, a Republican lobbyist at Navigators who overlapped for two months with Breaux at Patton Boggs. “In the two short months I was there, he was what you expect: very engaging, smart, substantive and very well-liked. He was an immediate fit into the firm.”

Christie said that Breaux maintained an open-door policy and will be missed on a personal as well as professional level.

“If in fact he goes and runs for governor, I think it would be a loss both of a kingmaker within Patton Boggs and also a personal loss for the people,” he said. “My friends who are still there just love working with him.”

A former colleague of Breaux said the one-time Senator, when he was in town, would often work from 7 in the morning until past 7 at night.

“It will be harder for them to get new business than it was when Breaux was there,” said this former colleague. “It’s a huge practice, so any one client or person isn’t going to sink it, but if there was one person you didn’t want to lose, it’s Boggs or Breaux. It’s going to be painful.”

Another lobbying firm that lost a key partner to a gubernatorial bid is Barbour Griffith & Rogers, the all-GOP shop whose founder Haley Barbour is now governor of Mississippi. When Barbour was on the campaign trail in 2003, his firm’s revenue went down to $11 million from almost $13 million the year before, but by 2004 it was up to $14 million.

“I think obviously Breaux has done extraordinarily well on the business generation side,” said yet another lobbyist with a competing law and lobbying firm. “While there may be a small short-term blip [if he leaves], a lot of infrastructure he has build will remain.”

Over the past year and a half, Patton Boggs has lost a number of key lobbyists, including a group of six that went to rival Pillsbury Winthrop Shaw Pittman, as well as Kathleen Means, a former Republican health care analyst on the Senate Finance Committee, and Daniel Kracov, a longtime health care lawyer and lobbyist at the firm, who went to Arnold & Porter.

And three knowledgeable sources said that Breaux’s contract at Patton Boggs was up at the end of the year. These sources said there has been speculation that Breaux, regardless of his gubernatorial bid, might not renew it.

Another lobbyist who runs the lobbying practice at a big law firm said Breaux was seen as someone who could be the public face of Patton Boggs and, internally, promote the vision of the firm, taking some of that load off Boggs.

“This will be a problem for them,” said this lobbyist from a rival firm. “If Breaux goes, and particularly if he wins or loses or doesn’t come back to the firm, it will be a huge blow.”

Lobbyists who have worked or do work with Breaux said that from the beginning he set out to work hard, even though he shares his time between ventures in New York as well. On his first day, one lobbyist said, Breaux went through the floors of Patton Boggs introducing himself to lawyers, paralegals, lobbyists and secretaries.

“Breaux came in with a very gregarious nature,” said one lobbyist. “He likes to be the life of the party.”

Joel Jankowsky, who runs the lobbying practice at Akin Gump Strauss Hauer & Feld, said that Breaux has helped Patton Boggs, but he said he expects the firm will carry on should Breaux depart.

“They will do well if John goes back and runs for governor,” he said. “I think whatever John wants to do, they’ll be very supportive.”

Offering a glimpse into Breaux’s vast D.C. fundraising network, Jankowsky said that he would “support John Breaux for anything. I haven’t been asked yet, but he’ll get lots of support from his friends in Washington.”