As President Bush and Sen. John Kerry (D-Mass.) work to portray each other as beholden to special interests inside the Beltway, each has turned to seasoned political pros from one of Washington’s most entrenched lobbying firms to run his political convention this summer.

Bush allies have tapped Larry Harlow of Timmons & Co. to lead a team of dozens of K Street lobbyists who will be in charge of everything from turning on the TelePromTer to massaging the schedule to ensure that Bush delivers his acceptance speech in prime time.

On the other side of the aisle, Tim Keating, a former Timmons lobbyist now with Honeywell International, will organize a separate group of lobbyists to help run the Democratic National Convention.

The decision by Republican and Democratic leaders to turn to the two lobbyists highlights a little-known element of convention trivia: Current and former Timmons officials have played key behind-the-curtain roles at every national political convention since Bill Timmons Sr. worked his first convention as a Young Republican four decades ago.

The streak is a testament to how much trust both political parties place in the nation’s oldest independent lobbying shop, as well as how dependent each side is on K Street lobbyists to orchestrate the conventions.

“They just breed a culture over there,” said Red Cavaney, president of the American Petroleum Institute and the man Harlow replaces in the convention role. “They feel that working at the conventions is an important thing to do.”

The founder of the firm, Timmons Sr., is considered the father of the modern, scripted convention.

This year, seven of the nine Timmons lobbyists will help organize the hundreds of Washington lobbyists and Congressional aides who will lend a hand in Boston and New York City.

At the Republican convention, Bill Timmons Jr. and the firm’s newest hire, John Kelliher, plan to work under Harlow on an elite team of a dozen political pros who script and stage the convention.

Tom Korologos, a former Timmons lobbyist now working in the Bush administration, will advise Harlow at the GOP convention after helping to run the last several conventions.

On the other side of the aisle, Timmons lobbyists Rich Tarplin, Dan Turton and Alan Hoffman will help their former colleague Keating by handing out credentials or working the cloakrooms at the Democratic National Convention in July.

Harlow said Timmons officials encourage the firm’s lobbyists to volunteer at the convention to support Bush.

“It’s all about re-electing George Bush,” Harlow said.

Working the conventions also gives Timmons lobbyists more influence back in Washington.

“It’s good for each of us to validate your support for the party and the candidate,” said Harlow. “That’s good for your effectiveness.”

But the job comes with perils. Lobbyists can sometime be placed in the awkward position of upsetting the very lawmakers they rely on to make a living in Washington.

“If you have to tell a Member of Congress who wants 30 minutes on the podium and you give them 5, you’ve got a sticky situation,” said Timmons Sr.

Indeed, lobbyists were forced to shoo then-Rep. Guy VanderJagt (Mich.), chairman of the National Republican Congressional Committee, off the stage during a speech that exceeded his time at the GOP convention a decade ago.

“A couple of times we’ve had to turn off the mic, put on a video and introduce the next speaker,” said one lobbyist involved in conventions.

To be sure, Timmons isn’t the only firm in town that plays a top role at the conventions.

Lobbyists at The Duberstein Group share a convention tradition that began when Timmons Sr. tapped Kenneth Duberstein to help him run the 1984 Republican Convention.

This year, Henry Gandy and Dan Meyer of The Duberstein Group plan to work under Harlow at the Republican convention.

Meanwhile, Mike Berman will serve as a senior adviser for this year’s Boston convention after taking a more active role at every convention since 1976.

Because Republicans and Democrats organize their conventions differently, the lobbyists at each will have a different focus.

Republican National Committee officials hire a professional staff to handle the sticky task of assigning credentials. But they lean on Harlow and his team of volunteer lobbyists and Congressional aides to script the made-for-television event and make sure the event sticks to the schedule.

“We’re supposed to make sure that the trains run on time,” Korologos said.

“It’s a huge job from soup to nuts, selecting speakers, the convention theme, coordinating speakers, orchestrating rehearsals, scripting, speechwriting and clearing everything with the White House,” said Pat O’Donnell of Venable, who has worked on GOP conventions dating back to 1972.

“If someone was getting paid for this, they would get a million dollars for three months’ work,” O’Donnell said.

In contrast, Democratic officials rely a bit more on a group of Hollywood producers for managing the stage, while Keating and a volunteer staff of dozens of lobbyists and Congressional aides keep the cloakrooms stocked and hand out credentials.

Keating said Washington insiders are good for the job because “they know who all the players are.”

His top lieutenants this year will include Tarplin; Chuck Brain of Capitol Hill Strategies; Steve Palmer of Van Scoyoc & Associates; John Orlando of the National Association of Broadcasters; Brian Griffin of Honeywell International; and Tom Keating, his brother, a lobbyist with the OBC Group.

Harlow’s senior staff includes Timmons Jr.; O’Donnell; Kelliher; Ed Ingle of Microsoft; Pam Turner, a former National Cable and Telecommunications Association lobbyist now with the Department of Homeland Security; Gary Andres of the Dutko Group; and Bob McKernan of Edelman.

Timmons Sr. and Duberstein have since retired from the convention business, though each will advise Harlow and his staff.

Timmons Sr. founded Timmons & Co. with Korologos in 1975 when they left the White House legislative affairs office in the Ford administration.

The firm started with 10 clients and charged a flat $100,000 annual fee. (Today, the firm has twice as many clients and its retainer — now $360,000 — has grown a bit less than inflation.)

The firm is now run by the 55-year-old Harlow, who began studying for his current role more than a decade ago when he helped out Cavaney.

Harlow grew up playing in the White House when his father, the legendary Republican operative Bryce Harlow, started the first White House legislative affairs office for then-President Dwight D. Eisenhower.

Harlow’s father worked his first convention in 1956 and played a central role in GOP conventions until 1980, when he helped broker the deal that put former rivals Ford and Reagan side by side on stage.