The United States says it has suspended some tests related to a proposed missile defense system, in order to adhere to the Anti-Ballistic Missile treaty. However, the United States still wants to abandon the treaty and move forward with an anti-missile defense because of the terrorist threat.

Defense Secretary Donald Rumsfeld said Thursday the Pentagon recently cancelled some anti-missile tests to avoid being seen as violating the Anti-Ballistic Missile treaty. Mr. Rumsfeld noted that some aspects of the 1972 pact, signed between the then Soviet Union and the United States, are open to differing interpretations. But he said that some planned tests of the proposed U.S. missile defense skirt the edge of the treaty's limits.

"On test activities such as these, as I have indicated, it is possible that someone could raise an issue because of ambiguities in the treaty," Mr. Rumsfeld said. "And we do not want to get into that debate. For some time now, we have advised the Congress and the government of the Russian Federation that the planned missile defense program was going to bump up against the ABM treaty," he said. "That has now happened."

President Bush wants to abandon the 1972 treaty altogether so the United States can proceed with the controversial missile defense shield.

Mr. Rumsfeld said the United States will not violate the treaty while it is still in force. But he said the Bush administration remains committed to its goal of jettisoning the pact, and that testing of some aspects of the anti-missile defense system will continue.

"The one thing that's clear is that the United States cannot stay bound to the constraints of that treaty and still do what we still believe very sincerely we must do, and that is to develop effective ballistic missile defenses," he said.

The U.S. defense chief said the issue will be a subject of discussion between Russian President Vladimir Putin and President Bush when the Russian leader visits the United States next month.

Russia has been a vocal opponent of the proposed missile defense. It wants to keep the ABM treaty in force, saying it is a stabilizing factor in global security.