Those following the debate over the New START treaty inked by Presidents Obama and Medvedev in April know that both governments dispute what it means. Russia says it'll impose real restrictions on U.S. missile defenses. U.S. officials brush off those claims.

The dispute centers on language in the preamble linking strategic offensive and defensive weapons and claiming such linkage "will become more important as strategic nuclear arms are reduced."

Treaty supporters in the U.S. say this language is merely rhetorical; it won't restrict our ability to defend against missiles from Iran, North Korea or elsewhere. It's stunning how easily they dismiss Russia's interpretation. They should review a little history. The Russians may know something they don't.

For example, under the 1972 Anti-Ballistic Missile (ABM) Treaty with the Soviet Union, the U.S. consistently placed limitations on "theater" (shorter-range) air and missile defense systems the treaty did not officially cover. Why? Because Pentagon attorneys feared controversy with the Soviets. Their guidance led the U.S. to "dumb down" the Patriot missile so that it could intercept only "slow and low" missiles, though nothing in the ABM Treaty required such design and testing limits. As a result, former Strategic Defense Initiative Director Henry F. Cooper confirmed later, "In the 1970s, no ballistic missile defense capability was given to [the developmental] SAM-D, now called Patriot."

So what's wrong with shaving a little capability?

It ultimately costs lives. Take the Gulf War. Between August 1990 and the war's outbreak in January 1991, the U.S. rushed to build new Patriot models to counter Iraq's Scud missiles. But they were far less capable than they could have been. More capable interceptors could have prevented an Iraqi missile from killing 28 American soldiers in Dhahran, Saudi Arabia, that February. Lives were lost because overzealous U.S. attorneys, wary of offending the Soviets, went far beyond the "letter of the law" of the ABM Treaty.

Democratic and Republican administrations also bent over backward to avoid violating ABM Treaty limits on testing systems "based on other physical principles." This provision was mistakenly applied to any new technology - particularly to anything for outer space, since that was what most rankled the Russians. The Pentagon intentionally slowed development of space-based defenses. We remain far behind what the technology will allow in space because of the years of dithering caused by the ABM Treaty.

A third example occurred after the Soviet Union collapsed. The U.S. negotiated so-called "demarcation agreements" with Belarus, Kazakhstan, Russia and Ukraine - states the Clinton administration sought to make our new ABM Treaty partners. Mr. Clinton wanted to maintain "the viability, integrity and effectiveness of the treaty" by theoretically giving free rein to U.S. theater missile defense systems, which everyone agreed we needed. But that didn't happen. By including some of the ABM Treaty's definitional language, the demarcation agreements ended up constraining theater defenses, most particularly the sea-based system the U.S. was developing.

Then Russia got into the act. It insisted the demarcation agreements be brought into force before it would ratify START II. But because the U.S. Senate was so opposed to the succession and demarcation agreements, Mr. Clinton submitted none of them for ratification. START II and the demarcation agreements died because the Senate wisely refused to let Russia hold our missile defense capabilities hostage to the promise of a strategic arms reduction treaty.

Granted, New START doesn't have the kinds of detailed restrictions on developing, testing and deploying defenses in the ABM Treaty and demarcation agreements. However, it does re-establish the linkage between offensive and defensive strategic forces that Russia went to the mat over in the 1990s.

Here is where history matters: As they did with START II and the demarcation agreements, Russians are vigorously pushing the Senate today to choose between U.S. offensive reductions and robust missile defenses.

And the Obama administration is playing this Russian game. It sacrificed the "third site" of U.S. missile defenses in Europe to counter missiles from Iran, mainly to mollify Russia. It scaled back the ground-based interceptors in Alaska and California from 44 to 30, mainly to convince China that our defenses pose no significant capability against their missiles.

As the threat of missiles launched from Iran, North Korea, or a rogue state grows, so does the need for more robust defenses. At some point, our need to defend against longer-range Iranian and North Korean missiles will run right up against the promise implied in New START that our systems won't have any capability against Russian missiles.

When that happens, someone in Congress will undoubtedly say this or that upgrade to our missile defenses violates New START. Or worse, a Pentagon attorney will say it, and nobody but a few vigilant experts will know better or care.

As the saying goes, those who ignore history are destined to repeat it. We've been down this road before, and it cost the country dearly.

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