Sen. Arlen Specter (search), one of the Republican Party's leading moderates, held a tenuous lead in Pennsylvania's GOP primary Tuesday in the face of a surprisingly stiff challenge from a conservative congressman who branded him a RINO — Republican In Name Only.

With 67 percent of precincts reporting, Specter led with 279,826 votes, or 52 percent, to Rep. Pat Toomey's (search260,013 votes, or 48 percent.

"I have covered all of Pennsylvania's 67 counties," Specter said shortly before the polls closed. "We faced up to the issues squarely. We have met the people, we have analyzed the projects, we have dealt with the issues. And there's nothing more that I could have done."

More than 90 percent of the precincts were reporting in Specter's home base of Philadelphia (search), where he led Toomey by more than 6,000 votes. Toomey was leading in the Pittsburgh area, where only about half of the votes had been counted, and he was winning by large margins in his home base in Lehigh and Northampton counties.

The race between Specter, 74, who was seeking his fifth term, and Toomey, 42, was expected to go down to the wire. Turnout among the state's 3.1 million Republicans was low.

The closely watched contest represented perhaps the most serious primary challenge to any Senate incumbent this season.

Toomey got within striking distance through a campaign that criticized Specter as too liberal on issues including abortion, but some leading conservative Republicans rallied to the incumbent's defense. President Bush and other administration officials campaigned with Specter, and Sen. Rick Santorum (search), R-Pa., hopscotched across the state with him Monday.

Many Republicans feared a Specter loss ultimately could cost them control of the Senate, where they hold a 51-48 majority, with one independent. Toomey could find it harder to defeat Rep. Joe Hoeffel, a three-term congressman from the Philadelphia suburbs who ran unopposed in the Democratic primary.

A Toomey primary win also could hurt President Bush's effort to win over much-needed moderate voters in Pennsylvania, a swing state with 21 electoral votes that Bush narrowly lost to Democrat Al Gore in 2000.

Toomey bucked GOP leaders in challenging the senator. Few considered him a threat as recently as last month, but a poll released on the primary's eve showed the congressman just 6 points behind.

Specter relied heavily on Bush's endorsement as he defended his record.

"I think it's very important to focus on what President Bush wants," Specter said after casting his ballot in Philadelphia. "He's the leader of the party. He thinks I can help him be re-elected." He added: "The Democrats are on the sidelines hoping that I lose."

Toomey started Tuesday greeting voters in Lancaster County and voted later in Zionsville, in eastern Pennsylvania's Lehigh County.

"I've been thrilled with the reaction from people I've gotten at the polls," Toomey said. "It feels very good."

Toomey, a three-term lawmaker, is a fiscal conservative, opposes abortion rights and has voted against an increase in the minimum wage and background checks for firearm purchasers at gun shows.

Specter, a former Philadelphia district attorney, often enjoys support from unions and abortion rights activists and has clashed with the White House over tax cuts and homeland security.

During the campaign, he touted his prowess in delivering hundreds of millions of federal dollars to Pennsylvania each year because of his 24-year tenure in Washington. He called Toomey too "far out" for the state.

Specter is in line for the chairmanship of the Judiciary Committee next year — a prospect that scares conservatives still smarting over his 1987 vote thwarting the Supreme Court nomination of Robert H. Bork.

Specter spent more than $10 million on his campaign, about three times as much as Toomey. But he also had to fend off a $2 million assault from the conservative anti-tax group Club for Growth, which put other GOP moderates on notice when it targeted Specter as its No. 1 priority this year.

The state's most competitive congressional race looked to be the one for the seat Hoeffel is leaving. Two Democrats and three Republicans battling it out in primaries had already raised a total of $2.75 million by April 7.

In Pennsylvania's 17th Congressional District, the son of Penn State football coach Joe Paterno, Scott Paterno, 31, held a narrow lead in a six-way Republican primary.

He was counting on his big family name to overcome his little political experience in one of the nation's most crowded primary fields for the House.

A campaign for a state House of Representatives seat, meanwhile, took a shocking turn Tuesday when one of the candidates apparently killed himself.

Sam Kovolenko, 46, one of five candidates in the Democratic primary for the seat, was found by his wife in the bedroom of their Ambridge home with a gunshot wound to the neck. Investigators believe Kovolenko committed suicide because a rifle was found by his body, there were no signs of a break-in and the door to the house was locked, Beaver County Coroner Wayne Tatalovich said.