WASHINGTON -- The triumph of conservative forces over the Republican Party establishment in upstate New York has emboldened like-minded activists, and it could drive the GOP sharply to the right as it lines up candidates for the 2010 midterm congressional elections.
 
The rebellion that drove a moderate Republican off the ballot in a special House election Tuesday is sending a clear message to the party leadership and its candidates: Ignore the conservative grass roots at your peril.
 
That message figures to resonate in the coming months in several congressional primaries and in races where third-party challenges are springing up and threatening to divide the Republican vote.
 
In Columbus, Ohio, a conservative has decided to run for the House because he does not see enough difference between Democratic Rep. Mary Jo Kilroy and her leading Republican opponent.
 
In southern Virginia, where Democratic Rep. Tom Perriello has been expected to face a tough fight for a second term, a conservative is campaigning against a Republican he considers a "RINO" -- Republican in Name Only.
 
The most prominent battlefield on which the conservative wildfire is spreading is Florida, where Gov. Charlie Crist, the GOP frontrunner for the Senate nomination in 2010, faces a challenge from a conservative former state House speaker, Marco Rubio.
 
That's why all eyes in the party will be turned toward the northern reaches of New York in Tuesday's elections. In the state's 23rd congressional district, voters face a choice between Democratic lawyer Bill Owens and conservative businessman Doug Hoffman. Hoffman's persistent charges the Republican Party's hand-picked candidate, Dede Scozzafava, was too liberal -- an assertion echoed by conservative activists across the country -- resulted in her dropping out of the race last weekend.
 
"If Hoffman wins this, it will be like dropping a bomb into the center of the Republican caucus," said David Keene, head of the American Conservative Union. "Conservative leaders are standing up and saying, 'On to Florida."'
 
Even if Hoffman does not win, experts predict big waves will rock the GOP.
 
"Win or lose, the conservatives will be emboldened and will look for other fights," said Stuart Rothenberg, a nonpartisan analyst of congressional elections. "I have no doubt in my mind that there are more to come of these tests."
 
Ken Spain, spokesman for the National Republican Congressional Committee, said the New York election sends a message that is perhaps more troublesome to Democrats than Republicans: The anger in the electorate is clearly not a mandate for the Democratic agenda.
 
"While the circumstances in this race are unusual, the one constant factor at play -- both locally and nationally -- has been that independent voters continue to peel away from the Democrats and (are) gravitating toward the right," Spain said.
 
Other major elections Tuesday include a race in Virginia, where Democrats have been struggling to retain the governor's office and Republican Bob McDonnell has been leading in the polls. In New Jersey, Democratic Gov. John Corzine is in a tight re-election battle against Republican Chris Christie, a former prosecutor. A third-party candidate in that race could affect the result.
 
The other special House election Tuesday will fill the seat of Rep. Ellen O. Tauscher, D-Calif., who was appointed President Barack Obama's undersecretary of State for arms control and international security. The Democratic nominee, Lt. Gov. John Garamendi, is leading in that race over his GOP opponent, David Harmer.
 
In New York, Mayor Michael Bloomberg is expected to easily win a third term.
 
The election in upstate New York has distinctive features that have given Hoffman an unusual advantage. Because only two districts are holding special elections in this political off-year, Hoffman attracted unusually intense attention. He won endorsements from Sarah Palin and other conservative celebrities, as well as a flood of campaign cash from outside the district. That kind of singular spotlight will be unavailable to outside candidates next year who will be part of a 435-district congressional election.
 
What is more, Scozzafava's nomination was especially provocative to conservatives because she supports legalized abortion, gay marriage and greater leverage for labor unions.
 
Conservatives' dismay and irritation at national Republican leaders may be more potent and consequential in the 2010 elections. The third-party challenges in the Ohio and Virginia House races come from long-shot outsiders. But if they gain even a modicum of traction, those candidates could undercut Republican strength against two of the party's top targets: Kilroy and Perriello are first-term Democrats who were elected by a hair's breadth last year.