In Pennsylvania's race for the U.S. Senate, both candidates face crucial challenges in holding onto core elements of their traditional party bases.

Democrats have crowed that Arlen Specter's conspicuous efforts to court conservatives in the primary he barely survived last week will weaken the crossover appeal that has traditionally allowed him to win votes from Democrats. That, however, does not appear to be the case with one central Democratic constituency, organized labor. Several prominent state labor leaders interviewed since the primary suggest that Specter remains the favorite, over Democratic nominee Joseph Hoeffel, to capture the endorsement of the state AFL-CIO, retaining the support from labor leaders that he enjoyed in his last general election victory against Democrat Bill Lloyd.

Conservative displeasure with Specter was amply demonstrated in Rep. Pat Toomey's nearly successful campaign to wrest the nomination from the four-term incumbent. On election night, Toomey nonetheless offered his "unequivocal'' support for Specter.

Conservative anger with the incumbent persists, however. On election night, in Toomey's local headquarters in a Bridgeville restaurant, the televised picture of Sen. Rick Santorum drew boos from some partisans bitter over his allegiance to Specter. Among the key questions about Specter's campaign is whether that anger will subside, and whether conservatives will have anywhere else to go if it does not.

Jim Clymer, a lawyer and former nominee for lieutenant governor on the ticket of the conservative Constitutional Party, said the party was determined to provide an answer to the second question. He said he and his Constitutional colleagues planned to collect enough signatures between now and August to field a conservative alternative to "the two liberal peas in a pod.''

Clymer, who is from Lancaster County, one of Toomey's stronger regions in Tuesday's balloting, ran with Peg Luksik in the 1994 and 1998 races for governor. He said that between the 500,000 Republicans who voted for Toomey and the ranks of pro-life Democrats, a Constitutional candidate would have a realistic chance of capturing the Senate seat. Clymer cited the successful 1970 Senate candidacy of James Buckley in New York as a precedent for conservative success in a three-way contest with more liberal major party nominees.

Clymer acknowledged, however, that he thought it was important simply to provide a conservative alternative to Specter, whom he described as the greater of the two evils of the major party nominees, "because he represents a greater threat to the Constitution.''

Hoeffel confronts dangerous fissures in his own partisan base because of Specter's traditionally strong ties to labor. Specter's particularly ardent embrace of President Bush and the conservative Santorum doesn't seem to have alienated the affections of the state's labor hierarchy.

The Republican has been endorsed by the state's politically active teachers unions, the Pennsylvania Federation of Teachers and the Pennsylvania State Education Association.

"For labor to function the way it should function, you can't endorse just Democrats," said Al Fondy, the longtime president of the PaFT.

The state AFL-CIO endorsed Specter in the context of the GOP primary only. Its leaders will meet in late August to determine an endorsement for the general election, and it appears that the best Hoeffel can hope for is for the group to stay neutral, as it did in 1992, when Specter barely survived a challenge from Democrat Lynn Yeakel. Even then, Specter's campaign benefitted from an endorsement by United Mine Workers leader Rich Trumka that was trumpeted by the Republican in his commercials.

"Right now, each candidate has some support. I would say Senator Specter has more solid support than Congressman Hoeffel," said Rick Bloomingdale, secretary-treasurer of the Pennsylvania AFL-CIO.

Bloomingdale said the Montgomery County Democrat had a better voting record than Specter, according to the AFL-CIO's congressional scorecard. But, he said, "It's hard for us to go against an incumbent who has been with us on some key issues."

He cited, as an example, Specter's position against the Bush administration on revisions proposed for overtime regulations.

"In addition to votes," he said, "he's been helpful with his [appropriations] committee seat in making sure things like OSHA and the NLRB are adequately funded."

The AFL-CIO's executive committee will meet in late August, to question each of the candidates and decide whether to make an endorsement in the race, a step that requires the support of two-thirds of the 59 members of its board.

Jack Shea, president of the Allegheny County Labor Council, pointed out that his umbrella group of local labor organizations has recommended Hoeffel's endorsement, but he said of the Democrats' prospects with the statewide labor body, "I really don't know what's going to happen."

In an appearance in Homestead this week, Hoeffel said that he remained confident that most of labor would eventually end up in his corner. Tom Hickey, a spokesman for his campaign, said, "There's a long debate ahead of us. Labor cares about health care, labor cares about jobs. Senator Specter doesn't have a plan to get any of those things done. Over the next seven months, that will become clear to every member of labor."

Labor's rank-and-file, of course, does not always follow the wishes of its hierarchy, a fact demonstrated in contests ranging from Ronald Reagan's two presidential elections to Gov. Ed Rendell's 2002 primary victory over Auditor General Robert P. Casey Jr. despite overwhelming opposition from labor leaders.

Bloomingdale said Specter could be the unintended victim of labor's political activism this year, even if he does manage to get the AFL-CIO's endorsement. That is because, Bloomingdale said, the Pennsylvania labor movement's first political priority will be to turn out votes against Specter's key primary ally, President Bush.

"Arlen has to worry about a huge Democratic wave at the polls,'' he said. "Because of all the anger out there, Kerry may be the first presidential candidate in a while that has some coattails.''