Cranston, R.I., Mayor Steve Laffey (R) has national Republican leaders on edge.

He has a really “BIG” announcement to make tonight, according to a flier his supporters distributed around the state over the weekend.

Most observers assume he will tell the crowd assembled at the Cranston Knights of Columbus Hall that he intends to challenge Sen. Lincoln Chafee (R-R.I.) in the Republican primary next year.

If so, GOP leaders wish he would just stuff his message down the large megaphone the cartoon character on his flier is holding.

“The timing of Laffey’s announcement tells us two things: Apparently his ego is so gigantic that he thinks his news is important enough that it could possibly draw attention away from the opening night game of the Super Bowl champion New England Patriots,” said one GOP official, who did not want to be named. “And he and his staff evidently didn’t notice that other politicians were taking the responsible course of action and postponing their political announcements in deference to the victims of Hurricane Katrina.”

Harsh words. But then, a party crasher really cannot expect red-carpet treatment when he enters the room and insults the host.

Chafee is arguably the most vulnerable Republican Senate incumbent this cycle, and party elders do not want him made more vulnerable by a bruising primary.

And that assumes Chafee can beat Laffey in the primary.

Rhode Island is overwhelmingly Democratic, but Republican primary voters are generally more conservative than the moderate Chafee.

Brown University political scientist Darrell West has predicted that as few as 25,000 voters could participate in the Republican primary and skew the results toward a conservative candidate like Laffey.

Independents, who make up about 50 percent of the state’s electorate and might be inclined to support Chafee in a general election, must choose one party’s ballot and often pick the Democrats’. Only about 10 percent of the voters are registered Republicans.

“If there is a Republican primary, Steve Laffey would be favored,” said Jim Hackett, a family friend of Laffey’s who sits on the Cranston Republican City Committee. “If there is a Republican primary, Lincoln Chafee should just leave.”

Chafee is not backing down and is prepared for a tough primary, according to his spokesman, Steve Hourahan.

“We’ve assumed we were going to have a Republican primary from the beginning,” Hourahan said.

The National Republican Senatorial Committee has made clear that Laffey should not count on them if he knocks off Chafee in the September primary.

“Senator Chafee is a valued member of the Republican caucus,” NRSC spokesman Brian Nick said. “Without a shadow of a doubt, he is absolutely the best person to ensure that his seat doesn’t fall into the hands of someone who would compete for the prize of most liberal Member of the United States Senate. Sen. Chafee will have the full support and resources of the NRSC to ensure that he is re-elected.”

Rhode Island Secretary of State Matt Brown and former state Attorney General Sheldon Whitehouse are competing for the Democratic Senate nomination. National Democrats are gleeful at the prospect that Laffey could defeat Chafee in a GOP primary.

The possibility that Laffey will take on Chafee has already caused the state Republican Party much consternation.

National Committeeman Robert Manning, a Laffey supporter, said the state party should not accept a $500,000 donation from the Republican National Committee if it is intended only for Chafee’s use.

Hackett said national party leaders should butt out of the primary and let it run its course.

“I really don’t think what the national party does is going to matter,” he said. “It’s a Democratic state; if the national party were too visible in their role it would backfire on them.”

The state party officially says it must remain neutral if a primary takes place.

“If a primary comes up, the party has an obligation to do what needs to be done to ensure that the primary process is done properly,” state GOP Executive Director Jeff Deckman said.

At least one deep-pocketed group may come to Laffey’s assistance.

“I’m not convinced anyone with an R after their name should get a free pass,” said Club for Growth President Pat Toomey.

The conservative, anti-tax group has already run ads targeting Chafee on the estate tax bill before the Senate. Even so, Toomey said his group has not decided whether to back Laffey.

“We have not made a decision as to whether or not we’ll get involved in that race yet,” he said.

Whether Laffey should defer to the national party’s wishes, Toomey answered: “You’re talking to someone who has a bit of personal history” of defying party leaders.

The former Pennsylvania Congressman angered the NRSC when he challenged Sen. Arlen Specter (R-Pa.) in last year’s primary because he thought Specter too moderate. Ironically, Specter is slated to be the headline attraction at a Washington, D.C., fundraiser for Chafee on Sept. 21.

While most political watchers expect Laffey to announce a Senate run tonight, rumors abounded Wednesday that he might decide to seek a different office.

Whatever he decides, people who know Laffey said he is not one to bow to pressure.

“He makes a lot of decisions based upon what he thinks is right, and he doesn’t really respond to outside influence,” one Republican insider who did not want to be named observed. “He goes regardless of what others want him to do … and if you show up to strong arm him, you’re making a mistake.”