About 1,000 politicians, lobbyists and Washington big shots in town for the Republican convention were treated to a private concert last night by a big-time band at one of the city’s hottest nightclubs.

The show at B.B. King’s, which cost a couple hundred dollars per head to stage, was headlined by ZZ Top and billed as being “as big and bad ass as the band’s home state” of Texas.

But this extravagant bash was not one of the dozens of events put together by New York City officials or convention organizers as a way of welcoming visitors to the Big Apple this week.

Rather, the party was organized by two Washington lobbyists who have hit a new chord in the influence business.

Republicans John Green and Jeff Kimbell, the lobbyists who put together the ZZ Top show, belong to a tiny but growing cadre of lobbyists, fundraisers and political operatives who have stepped into a vacuum created by campaign-finance reform. They and other lobbyists are the brains and muscle behind many of the big-ticket parties that punctuate the national political conventions.

“There is a new cottage industry of putting together these convention parties that did not exist at the last convention,” said Kirk Blalock, a Republican lobbyist with Fierce, Isakowitz & Blalock.

That cottage industry was made possible by the 2002 McCain-Feingold campaign finance law, which turned the convention party business on its head by barring the Republican National Committee, the Democratic National Committee and lawmakers from raising and spending soft money.

Official Washington, suddenly unable to ask corporations to chip $100,000 or more to hire a well-known band or to cover a big bar tab, exited the party business.

Enter the lobbyists.

Because “you can no longer throw a party to raise money for the Republican Party or the Democratic Party,” outside groups are planning “the events that the national parties have traditionally put together,” said Brandon Winfrey, a Republican fundraiser who is organizing several marquee events at this year’s convention.

This week will feature as many as 50 major parties and private concerts. But unlike the 2000 convention in Philadelphia, nearly all of of them are being organized by Washington lobbyists.

“It seems like everyone is on the concert bandwagon now,” said Rob Jennings, a GOP fundraiser who organized one of the first privately financed convention concerts four years ago.

This year’s party scene kicked off Sunday night with a Lynyrd Skynyrd concert for 2,000 at CroBar, put together by fundraisers Jennings and Winfrey.

The Grand Old Party will wrap up later this week with a dual performance by rap-rocker Kid Rock and country music star Trace Adkins. The show was organized by lobbyist Geoff Gray and the major music labels.

In between are concerts tonight by country music star Martina McBride, staged by AFLAC lobbyist Gina Rigby; a Wednesday-night show featuring the Marshall Tucker Band, Dickey Betts & Great Southern and Super Diamond thrown by Green and Kimbell; and nightly performances by cover band Duck Soup at a bash known as “Warehouse Party.” The Warehouse parties have been put together during the last two Republican conventions by lobbyists Bruce Gates and Henry Gandy.

“There are fewer ways to get noticed at a convention because of campaign finance reform, so people are looking for opportunities to attach their names to fun events,” Winfrey said.

“We wanted to offer our friends an opportunity to come and enjoy some good live music after they have been at the convention all day, have a drink and not worry about business,” added Green, a jovial Mississippi native who counts Pfizer, U.S. Tobacco, BellSouth and Citigroup among his clients.

Of course, planning a party isn’t just an altruistic act. It also can be good for business.

Right off the top, the lobbyist and fundraisers who throw the parties can turn a profit. Usually this happens by selling tickets and the right to be a sponsor of the concert to corporations and other lobbying shops. If they keep costs low, they can earn a pretty penny.

For $100,000, sponsors of the party thrown by Green and Kimbell got 100 tickets and 25 VIP tickets to both the Monday and Wednesday night performances. A donation of $50,000 bought 50 tickets and 12 VIP passes.

The pair rounded up more than two dozen sponsors and got lobbyists for Anheuser-Busch, UST and Allied Domecq to supply enough beer, wine and liquor to last for 11 hours of open bar over the two nights.

Overall, the two nights at B.B. King’s will cost $500,000 for Green and Kimbell, who say they simply hope to break even. In 2000, Jennings earned just $2,000 for a Lynyrd Skynyrd and Blues Traveler concert that cost $220,000. But even if they don’t earn a dime this way, the lobbyist-promoter could profit in another way.

By mounting a marquee event, lobbyists and fundraisers establish themselves as power players at the convention — people who are able to gain chits with Members of Congress, Congressional staff and clients by doling out tickets to exclusive events.

“If you have the money and don’t mind spending it, then you can make a tremendous statement with a concert,” said one Republican lobbyist. “If you are a national corporation and you want to take care of the Colorado delegation, why not invite them to your ZZ Top show?”

Green acknowledged that he decided to throw his own party partly to “create my own juice.” Indeed, during a lunchtime talk about the party, Green received a phone call from a scheduler for Sen. Gordon Smith (R-Ore.) who asked for a pair of tickets to the party.

At Sunday’s Lynyrd Skynyrd show, corporate sponsors, such as the Southern Company, AT&T and Raytheon, were able to hand out tickets to more than a dozen lawmakers.

Among those who attended the “Southern Tribute” were Gov. Haley Barbour of Mississippi, Sen. John Cornyn of Texas and Reps. Mark Foley of Florida, Jim Gibbons of Nevada and Marsha Blackburn of Tennessee.

This role reversal upsets government watchdogs. “It’s a way of currying favor, lobbying, gaining access and networking all at the same time — all of which is important when they have legislation up in front of any of these people,” said Larry Noble of the Center for Responsive Politics, a nonpartisan watchdog. “They are doing it because they see it as an investment and they want to see a monetary return on that investment.”

Despite the rewards, pulling off a show like the ZZ Top concert can add up to an enormous investment of time.

Green and Kimbell started laying plans for their parties the day after New York City was announced as the site of the convention last year. Even something as straightforward as booking a band can prove tricky when throwing a concert during a political convention.

The duo’s first choice, the Allman Brothers, backed out once they found out that they would be playing to a Republican crowd. Van Halen’s David Lee Roth said his band no longer plays private shows.

“More than half of the artists are Democrats,” said Jennings. “And even the ones that aren’t are reluctant to be viewed as partisan since the industry is so Democratic.”

To land ZZ Top, Green and Kimbell veiled the fact that the party would be widely attended by Republicans. They removed the images of elephants from the invitation and bagged the idea of holding the concert in honor of certain Republican lawmakers. Said Green: “We worried about ZZ Top thinking that it’s political.”