ALTOONA, Pa. -- Outside the TV studio where two U.S. Senate candidates were about to debate, Paul Good was smiling through the chill drizzle. ''We finally have a chance to get Arlen Specter out of the Senate,'' he said.

Good is a Republican. So is Specter. But the Grand Old Party is having a family feud this spring in a state where it needs key victories in November to help Republicans maintain control of the White House and the Senate.

With a small group of fellow Republicans, Good stood in the rain to show support for Pat Toomey, Specter's challenger in the April 27 primary. The three-term congressman, 42, is proving a surprisingly strong candidate. Specter, 74, is seeking a fifth term. He has drawn intense opposition from conservatives in and outside the state.

President Bush is backing Specter even though they've been at odds on some key issues. Specter opposes the president's limitations on stem-cell research. He is skeptical of the White House effort to rewrite overtime regulations. He voted to reduce the Bush tax cuts. He doesn't think the federal government should ban abortions and he's cool to a constitutional ban on same-sex marriages.

Presidents usually support incumbents of their own party, but the all-out enthusiasm of the White House in this case is notable. Vice President Cheney, chief of staff Andy Card and Bush political adviser Karl Rove all have helped Specter raise money. Bush is expected at a fundraiser in Pittsburgh on April 19. Other Republican icons -- Ed Meese, attorney general for President Reagan, former judge Robert Bork and former presidential candidate Steve Forbes -- have headlined fundraisers for Toomey.

The race has turned into one of the toughest of Specter's nearly four-decade career. It's an ideological battle that highlights the split between the Republican Party's moderate and conservative wings. It's also emblematic of the internal debate party strategists are having about how best to ensure the president's re-election.

Specter personifies the philosophy of those who believe that Bush needs to moderate his platform and persona to win independent voters and some Democrats. Toomey is the darling of conservatives who want the president to emphasize tax cuts, free-market economics and traditional family values to energize his Republican base.

Each candidate insists he can help Bush win Pennsylvania. The president lost the state by 5 percentage points in 2000 and is working hard to win its 21 electoral votes this year. Bush's trip to Pittsburgh will be his 27th visit to Pennsylvania as president. Toomey, whose grass-roots campaign is winning praise even from some Specter supporters, says he'll bring a flood of enthusiastic conservatives to the polls: ''All the energy of the campaign is with me.''

But even some Republican conservatives think Specter strengthens the ticket. ''Arlen can reach people who may not go to events for the president,'' state Sen. John Pippy says. Among those are voters in the Philadelphia suburbs, Specter's home turf and a key to a Republican win in Pennsylvania.

Specter's is one of 34 Senate seats up in this election: 19 are held by Democrats and 15 by Republicans. Toomey's backers say he'll strengthen the party's one-vote majority in the Senate by being a more reliably Republican vote. They say the state's other Republican senator, Rick Santorum, has proven that a conservative can win in Pennsylvania.

But Santorum is supporting Specter. He says his Senate colleague has the best chance to defeat the Democratic candidate, suburban Philadelphia congressman Joe Hoeffel, in a state where Democrats still hold a slight lead in voter registration. ''I want to win,'' Santorum says.

Specter should be invincible: As of last month, he had more than $9.2 million in his campaign treasury; Toomey had just over $2 million. The Keystone Poll, released last week, showed Specter with a 13-percentage-point lead among likely primary voters. More than half of those surveyed said they didn't know enough about Toomey to have an opinion of him.

Even so, Specter is ''clearly worried,'' says Rick Bloomingdale, secretary-treasurer of the Pennsylvania AFL-CIO, which has endorsed him. ''He's running as hard as if it were his first election.''

One reason for the senator's concern: With the presidential nominations locked up, there's little interest in the primary. ''If only conservatives show up at the polls, it's possible Arlen could face an upset,'' says Rep. Phil English, R-Pa., who supports Specter.

Another complicating factor: outside money. The Club for Growth, an organization that supports free-market fiscal policies and lower taxes, has mounted a $1 million ad campaign on Toomey's behalf. Club for Growth members have given another $775,000 to his campaign. The Main Street Republican Partnership, a group of moderate Republicans, is responding with $225,000 in contributions to Specter from members and about $100,000 in ads.

Both candidates have blue-collar backgrounds. Specter's father was a tailor and junkyard owner. Toomey's laid cable for an electric company. Both sons got Ivy League degrees. But the generational contrast is stark.

Specter began his public career with the investigation of President Kennedy's assassination, an event that occurred just two years after Toomey was born. As a staffer for the Warren Commission, he helped develop the single-bullet theory, which held that Lee Harvey Oswald was the sole gunman. When Specter was elected to the Senate in 1980, left-of-center Republicans like him were a third of the party's Senate caucus; now, Specter represents an increasingly rare species.

Toomey is a committed conservative who votes against labor's positions in a state where many politicians dare not do that. He backs free-trade deals even though his district, a former steelmaking area, has seen many jobs go overseas. Toomey accepted $500 from Republicans for Choice, an abortion rights group, in his first congressional race. Now, leading abortion opponents back him. He says his 3-year-old daughter's birth convinced him that ''I had to have a consistently pro-life record.'' 

In the end, weather may be the deciding factor. Fewer than 600,000 of the state's 3.1 million Republicans voted in the past two statewide primaries. For both candidates, says Pittsburgh political analyst Jon Delano, ''Turnout will be key.''