Facing a conservative challenger in a tightening re-election race, Sen. Arlen Specter (search) staunchly defended his independent voting record Monday and said it is important to have centrist Republicans in a gridlocked Senate.

Specter also said the growing controversy over what the government knew — and did — before the Sept. 11, 2001, terrorist attacks would give "black eyes all around."

In a 75-minute interview with Associated Press reporters and editors, Specter touted his 24-year record in the Senate and defended his evolving positions on the death penalty for Saddam Hussein, President Bush's tax cuts and judicial appointments.

The issues have all provided ammunition for conservative Rep. Pat Toomey (search), who is giving Specter, seeking his fifth term, the most serious primary challenge to a sitting senator this year.

The April 27 race is being carefully watched as the Republicans' slim 51-seat majority in the Senate hangs in the balance. It also is considered a litmus test of the strength of the GOP's right wing by national conservatives who are pouring more than $1 million worth of contributions and attack ads into the state to help Toomey.

"I am not a flip-flopper," Specter said. "I have voted 8,000 to 9,000 times, and you can find a rare occasion where I may have shifted a position when the terrain has shifted."

But "I learned a long time ago that when you want to get something done in Washington, you have to cross party lines," he said. "And my opponent's using that against me, too.

"It's very important to the country there be a center of the Republican Party."

Specter's appeal to moderate Republicans is considered an asset to President Bush's campaign in Pennsylvania, a swing state this election year. Bush will make his 27th visit to the state next Monday at a Pittsburgh rally for Specter.

Specter acknowledged that the ongoing controversy over the Sept. 11 commission could hurt Bush in November. He said blame should be shared by former President Clinton.

"I think that there are going to be black eyes all around, on Clinton and on everybody," he said.

Specter also said "it was a mistake" to prohibit the government from negotiating with pharmaceutical companies for lower prescription drug costs. "I think that'll be revisited and it'll be changed," he said.

On Monday, Toomey's campaign continued taking aim, accusing Specter of flip-flopping on gambling, noting the senator's campaign is distributing fliers identifying him as a gambling foe even though he worked last year to help Indians open a California casino.

"The record clearly shows that Arlen Specter has aggressively supported expanding casino gambling," said Toomey spokesman Joe Sterns. "You just can't trust what he says."

Specter, who is in line to become the next chairman of the Senate Judiciary Committee, heatedly denied wanting to expand gambling. He said he was simply protecting the interests of some Pennsylvanians who invested in the project.

"I've been opposed to gambling forever," he said. "There was going to be gambling at that casino no matter what happened."