This year's presidential race isn't just overshadowing the U.S. Senate contest in Pennsylvania. The Bush-Kerry race is also shaping the battle between Republican incumbent Arlen Specter and Democrat Joe Hoeffel.

Specter is attempting a difficult balancing act, appearing alongside President Bush at campaign rallies while stressing his independence to moderate Democrats.

Hoeffel is clinging tightly to the campaign of Sen. John Kerry, hoping his party's presidential candidate will wear coattails in Pennsylvania.

With Republicans holding a 51-48 advantage in the Senate, control of the upper house could hinge on the outcome of the Specter-Hoeffel race. But presidential politics are creating the context for the contest.

"For a Senate candidate, the trouble with running in a presidential year is that you have less control over events," said Larry Ceisler, a Democratic political analyst and Duquesne law school graduate. "If Kerry is going to win the state by double digits, then Specter would rather not be running."

But if Kerry loses Pennsylvania -- most polls now show the two running neck and neck -- then he will surely take Hoeffel down with him.

In an interview with The Associated Press last month, Hoeffel said, "I need Kerry to win the state."

When interviewed Friday, he wasn't quite as blunt, saying, "I think I will be greatly helped by John Kerry's strength in Pennsylvania."

Banking on a Kerry victory in Pennsylvania, Hoeffel hopes that the vote totals in his contest will closely correspond to the numbers in the presidential contest.

"Hoeffel wants everyone who votes for Kerry to also vote for him," Ceisler said. "That's the only way he can win."

To achieve that goal, Hoeffel, a three-term congressman from Montgomery County, has tied his campaign to Kerry's, making joint appearances across the commonwealth and staking similar positions on the issues.

At the same time, Hoeffel is trying to link Specter to Bush in the minds of voters.

"Arlen Specter has been very loyal to George Bush," Hoeffel said. "By his own account, he votes with George Bush 89 percent of the time."

But Hoeffel realizes that some number of Kerry voters will split their tickets and vote for Specter. To compensate, he is counting on Constitution Party candidate Jim Clymer to draw a like number of voters away from Specter.

Hoeffel cannot realistically expect Clymer to garner more than 4 percent, or about 200,000 votes. Which means he must keep Democratic defections to a minimum to have any hope at all of beating Specter.

In other words, he must do better than Ron Klink, the Democratic candidate in the last Senate race in Pennsylvania.

Klink could not have asked for a better showing from his party's presidential candidate, Al Gore, who won Pennsylvania by more than 200,000 votes.

But more than 330,000 Gore voters snubbed Klink, handing a victory to the Republican incumbent, Rick Santorum.

As a familiar figure in the Democrat-rich and rich-Democrat Philadelphia area, Hoeffel figures to run a better-funded campaign than Klink did.

But Specter, armed with the endorsement of the state AFL-CIO, could conceivably attract even more Democratic voters than Santorum did.

In his last three elections, Specter collected more votes than the Republican at the top of the ticket: gubernatorial candidate Tom Ridge in 1998, President George H.W. Bush in 1992 and gubernatorial candidate William Scranton III in 1986.

Based on that pattern, George W. Bush would have to lose big if Specter is to be defeated.

G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College, doubts that Kerry can score a big enough margin of victory in Pennsylvania to carry Hoeffel and the rest of the Democratic ticket.

"It's not like there will be a huge landslide here," Madonna said. "It's a dead heat for the presidency.

Specter, in his bid to become Pennsylvania's first five-term senator, has been concentrating on shoring up his support among moderate Democrats, touting the endorsement he received from the AFL-CIO, the state's largest labor federation.

"When you get right down to it, [Specter] is in the center, where he has always been," said Christopher Nicholas, the senator's campaign manager.

In wooing moderates, Specter can't make much use of his party's conservative presidential candidate.

"Among Arlen Specter's natural base of moderate Republicans and moderate Democrats, President Bush is a liability, unless [a voter's] No. 1 issue is the war on terrorism," Ceisler said.

But in his bruising primary election battle with conservative challenger Pat Toomey, Specter enlisted the help of Bush, who spoke in a campaign commercial in the senator's behalf.

For the Nov. 2 general election, Bush could possibly draw Toomey voters back into the Specter fold.

Like Kerry and Hoeffel, the president and Specter have appeared together at several campaign rallies.

But it might not be necessary for the president to do anything more overt in Specter's behalf, according to Leslie Gromis Baker, Bush's campaign coordinator for the mid-Atlantic region.

"At this point, we don't see the Senate race as that close of a race," Gromis Baker said.

In a Quinnipiac University poll of 1,430 Pennsylvania voters, Kerry was leading Bush 47 percent to 42 percent last month, while Specter was leading Hoeffel, 48 percent to 33 percent.