Even large-scale Russian cheating on a new nuclear arms treaty would not hurt U.S. security because U.S. nuclear strengths would more than offset any Russian violations, the Obama administration has concluded.

James Miller, the Pentagon's leading authority on nuclear arms, on Tuesday outlined for the Senate Armed Services Committee how the administration came to this previously undisclosed conclusion.

He was challenged by Sen. John McCain, R-Ariz., who asked in an incredulous tone why the Obama administration bothered to negotiate the treaty if Russian cheating is of no consequence.

"Why have a treaty?" McCain boomed.

"To say that (Russian cheating) has little, if any, effect, then we've been wasting a lot of time and money on negotiations," he added.

After the hearing, Miller told The Associated Press that the U.S. does not have, nor does it seek, nuclear superiority over Russia.

"The U.S. has tried to be clear ... that we desire approximate parity with Russia, not nuclear superiority," he said.

The ability to verify compliance with the treaty is a key point of debate as the Senate considers whether to ratify the deal, which was signed in April by President Barack Obama and Russian President Dmitry Medvedev. Both governments hailed it as a major breakthrough in U.S.-Russian relations and a step toward making the world safer.

The treaty, known as New START, would shrink the limit on strategic warheads to 1,550 for each country, down about a third from the current ceiling of 2,200. It requires approval by the legislatures of both nations; the Russian Duma is waiting for the U.S. Senate to act first.

Prospects for ratification are considered strong for the treaty, which has drawn wide bipartisan support among think tank experts and former top-ranking officials. But Senate approval might not happen until this fall.

Miller told the committee that the size and structure of the U.S. arsenal of strategic nuclear weapons — the so-called triad of submarines, bomber aircraft and land-based launchers — provide assurance that any Russian cheating would have little military significance for the U.S.

"Because the United States will retain a diverse triad of strategic forces, any Russian cheating under the treaty would have little effect on the assured second-strike capabilities of U.S. strategic forces," Miller said. He added that he does not believe Russian cheating is likely.

The ability of U.S. missile-bearing submarines and bombers to survive any Russian first strike, and to deliver a devastating counterstrike, would be "unaffected by even large-scale cheating" by the Russians, Miller said. That fact will discourage Russia from trying to secretly exceed the pact's limits on warheads, he said.

What's more, in a crisis the U.S. would be able to add extra nuclear warheads to missiles aboard submarines and bombers — a capability the Russians apparently do not have, Miller said.

"Therefore any breakout scenario would have, at most, limited military significance," he said.

Miller later said any cheating would be politically significant and unacceptable, but he did not elaborate.

Although he did not say so in his testimony, Miller's remarks reflected the conclusions of a classified State Department report to the committee on enforcing the treaty. The report has not been released publicly, but Sen. Carl Levin, the Armed Services Committee's chairman, read unclassified portions aloud at the hearing.

"Given the terms of the New START treaty, the potential benefits to be derived by Russia from cheating or breakout from the treaty would appear to be questionable," the report said.

A copy of the unclassified passages of the State Department report was provided to The Associated Press after the hearing by the Republican side of the Armed Services Committee.

The report is dated July 12.

"The costs and risks of Russian cheating or breakout, on the other hand, would likely be very significant," the report said. Russia would face financial and international political costs if it violated the treaty's provisions, with little to be gained militarily, it said.

Air Force Gen. Kevin P. Chilton, commander of U.S. Strategic Command, which is responsible for ensuring the viability of the U.S. nuclear arsenal, said he agreed with Miller that the United States could adequately defend itself in the event Moscow ignored the treaty's limitations.

"I believe that we are in a good position" with the Russians in that regard, Chilton said.

"Well, what this brings to the casual observer's mind, general, is that if it doesn't have any consequences if they do any cheating, what's the point of having a treaty?" McCain asked in response.

McCain's point was a reminder of the Bush administration's initial approach to nuclear arms control with Russia, which put little stock in negotiating a detailed treaty. It saw little prospect of the Russians managing a sudden, large-scale buildup of their nuclear arsenal, and so it preferred to set broad disarmament goals with the Russians instead.

Late in his second term, however, President George W. Bush did propose a new, more detailed nuclear treaty with Moscow.