"It could turn out to be a great treaty," Chairman Joseph R. Biden of the Foreign Relations Committee declared.

The complaints ranged from not requiring the destruction of the warheads to be taken out of U.S. and Russian arsenals over the next 10 years to exempting battlefield nuclear weapons from the cutbacks.

But in the first round of the Senate's review of the agreement Bush reached with Russian President Vladimir Putin in May, only one of the four critics, Sen. Russ Feingold, D-Wis., appeared on the verge of opposing the pact.

With Secretary of State Colin Powell in the witness chair, defending the treaty as a milestone in a new relationship with Russia, Feingold hotly questioned a provision that permits either side to abandon the accord with three-months notice and without explanation.

Arguing the Senate should be consulted first — and should have been before Bush scrapped a 1972 treaty that banned national anti-missile defenses — Feingold told Powell, "The administration is not taking the Senate's role seriously."

Challenging the administration from another direction, Sen. John F. Kerry, D-Mass., said the cutbacks should have been much deeper than the planned reduction from about 6,000 warheads on each side to 1,700 to 2,200.

Kerry said "the most glaring hole in this treaty" was that the warheads would not be destroyed but could be kept in storage — and easily put back on the launchers, bombers and submarines from which they were removed.

Kerry also said that keeping a stockpile of at least 1,700 warheads was in excess of the needs of the United States and Russia in their new relationship — and too many to have around with terrorists on the prowl.

But Powell told the Committee he believed the two sides would destroy many of the warheads they set aside. "There is no incentive to keep weapons we do not need," he said.

And yet, Powell disclosed the Bush administration was aiming for an arsenal of 4,600 long-range nuclear warheads, including some 2,000 warheads that are being held in reserve.

"This tells us the Bush administration wants to maintain flexibility and be able to double the size of the strategic arsenal under the treaty," Daryl Kimball, executive director of the private Arms Control Association, said.

He said the treaty was likely to pass but the Senate may be interested in adding "constructive conditions that fill in many gaps in this very sparse and incomplete treaty."

These, Kimball said, could require tougher provisions to ensure the terms are carried out and for the destruction of warheads.

Chairman Biden and a senior Republican, Sen. Dick Lugar of Indiana, called the treaty a good first step.

"I think this is a good treaty," Biden said. "It could turn out to be a great treaty or it could turn out to be marginal one."

Among the flaws Biden found in the pact was that it permits Russia to retain SS-18 multiple-warhead missiles that had been outlawed in the START II treaty that Bush's father, President George H.W. Bush, signed in January 1993.

Lugar called the treaty "a tremendous step in the right direction," but he said he also was concerned about not requiring the destruction of warheads and said "we must work with Russia to make sure they do not fall into the wrong hands."

Lugar, who has sponsored legislation to help Russia eliminate part of its nuclear arsenal, urged Congress to help cut delays in dismantling nuclear weapons by dropping a requirement that the White House demonstrate that Russia is committed to the goals of arms control.

Powell endorsed the idea.