The Obama administration's drive to win Senate approval of the New START arms treaty with Russia has hit a speed bump. Several senators are asking to see the secret negotiating record from the administration's official talks with Russia.

Why? Because U.S. and Russian officials publicly disagree about what the treaty says. Senators have a right to know - before they consent to ratification of a treaty that affects national security - how those terms now at issue were handled during the negotiations.

The differences regarding missile defense are stark. Russian Foreign Minister Sergei Lavrov asserts that the treaty links arms reduction to restraint on missile defense and that this linkage is legally binding. Russia, he says, can withdraw from the treaty if "the U.S.'s build-up of its missile defense strategic potential in numbers and quality begins to considerably affect the efficiency of Russian strategic nuclear forces."

Conversely, Secretary of State Hillary Rodham Clinton insists that the treaty "has no restrictions on our ability to develop and deploy our planned missile defense systems or long-range conventional strike weapons now or in the future."

However, in a "fact sheet" released about two weeks after Mrs. Clinton's claim, the State Department seemed less confident of her sweeping statement. The treaty "does not constrain the United States from deploying the most effective missile defenses possible," the State Department said.

But there's a big difference between "no restrictions" and those that may, in the administration's opinion, merely affect effectiveness. In fact, the State Department's fact sheet statement implies that concrete and practical limits could indeed be placed on missile defenses if Russia complains they affect their forces in some way.

Furthermore, there are reports that U.S. negotiators actually told the Russians that the U.S. had no intention of putting strategic missile defenses in Europe. Only a careful review of the negotiating record can set the record straight.

Mrs. Clinton recently misspoke when she testified that a Senate request to review the negotiating record would be unprecedented. In the past Democrats have asked for the negotiating records on the ABM Treaty and also the Intermediate Range Nuclear Arms Treaty. Sen. John Kerry of Massachusetts may assert that these requests were not intended to establish a pattern, but he would be on firmer ground if the Senate did not apply this standard only to requests made by Republicans.

This is no mere academic exercise. When the Reagan administration asserted that a careful reading of the negotiating record for the ABM Treaty substantiated a broader interpretation on testing than was hitherto applied, Senate Democrats led by Sam Nunn demanded full access to the negotiating record. They hoped it would disprove the administration. It didn't.

History shows how important it is to know exactly what the Russians claim when it comes to missile defense. The Soviet Union supported a narrower interpretation of the ABM Treaty, even as it was secretly violating that treaty. Today, Moscow has made it clear that it sees the New START agreement as practically limiting what we can do to defend ourselves against ballistic missiles.

We can dismiss those claims all we want. But if the Senate were to vote for ratification of the treaty without knowing what assurances - if any - were made by U.S. negotiators, it would open the door for Russia to insist that we are perpetually in violation of it. Should we attempt to deal with, say, a future Iranian missile threat by expanding missile defense capabilities in Europe, Russia could invoke these assurances and accuse us of violating the treaty.

Who cares what the Russians say? The Obama administration does. It's the leitmotif of its "reset" strategy toward Russia. Even without an arms treaty, the administration bent to Moscow's will and sacrificed missile defense sites in the Czech Republic and Poland.

If it would do that voluntarily, what would it do if Russia were to level charges of treaty violations? Every missile defense opponent would claim the effort to defend ourselves and allies endangers "the arms control process" and undermines U.S.-Russian relations.

Russia will doubtless continue to press for additional arms negotiations to formalize and expand limitations on our missile defense. At some point it will likely ask either for separate negotiations on missile defense or for a START follow-on treaty focused on U.S. missile defense systems.

We should not sacrifice our ability to defend Americans. No treaty should hinder the future development, testing and deployment of U.S. missile defenses. There can be no ambiguity or uncertainty about this. The current debate over missile defenses reflects deeper and even more troubling aspects of this treaty. For the sake of just getting a treaty, the president signed an instrument that establishes Russia as a dominant nuclear power; limits America's ability to respond to future threats; and will likely start rather than deter a future arms race.

Kim R. Holmes, a former assistant secretary of state, is a vice president at the Heritage Foundation.