The government should consider a tax on oil companies if they make excessive profits amid rising gasoline prices, a leading Republican senator said Sunday.

Pennsylvania Sen. Arlen Specter, chairman of the Senate Judiciary Committee, said a windfall profits tax, along with measures to stem concentration of market power among a few select oil companies, could offer eventual relief to consumers hurting at the gas pump.

"I believe that we have allowed too many companies to get together to reduce competition," Specter said.

"They get together, reduce the supply of oil, and that drives up prices," he said. "In the short run, it's hard to deal with it for tomorrow. But I think windfall profits, eliminating the antitrust exemption, considering the excessive concentration of power are all items we ought to be addressing."

Specter is backing legislation that would strengthen antitrust laws on oil company mergers after his committee held a hearing last month examining the growing consolidation of the oil industry. The nation's largest oil companies, including Exxon Mobil Corp., have denied their industry size has affected prices.

Last week, crude-oil prices hit record highs and average gasoline prices nationwide neared $3 a gallon.

Sen. Carl Levin, D-Mich., said he believes gas prices "would come down within a matter of days" if President Bush told oil companies that he was going to support a windfall profits tax.

"But the president will not call the oil companies into his office because he's been too closely allied with those oil companies, and if he does it's going to be a window-dressing conversation," said Levin, who appeared with Specter on CNN's "Late Edition."