In a major policy reversal, the United States Wednesdayformally linked any reduction in strategic nuclear weapons to the full dismantling of a Soviet radar array in Siberia.

The new hard-line position clearly involved a decision at the highest levels of the Reagan administration with all questions referred to Washington.An American arms delegation statement denounced the still-incomplete radar at Krasnoyarsk as a violation of the 1972 Anti-Ballistic Missile treaty.

It said strategic arms cuts are "impossible" unless the facility is destroyed and additionally warned that Washington "reserves all its rights" to possibly repudiate the ABM treaty because Krasnoyarsk is a "material breach" of its terms.

Unlike Moscow, the United States never previously tied agreements at Strategic Arms Reduction Talks (START) to other offensive or defensive weapons systems.

It always rejected Soviet linkage since talks began in 1985 between the aim of 50 percent cuts in long-range nuclear weapons and strict limits on the U.S. Strategic Defense Initiative, known as `Star Wars.'

Moscow similarly charges that any advanced SDI testing would violate the ABM accord which should be extended with "strict compliance" for at least nine or 10 years.

The new U.S. position was announced after a week of inconclusive talks at the third five-year review of the ABM treaty.

It was unclear if the linkage and implied threat to renounce the treaty could bind either Republican Vice President George Bush or Democratic contender Michael Dukakis when one of the two becomes president in four months.

U.S. arms spokesman Terry Shroeder was authorized to issue only a short reply to that and other questions about the policy switch.

"Because of the seriousness of the issue, including the potential for a declaration by the United States of a material breach (of the ABM treaty), we are referring all questions to Washington," Shroeder said.

The U.S. hard-line approach came in a sharp statement at the end of the fruitless ABM treaty review meeting.

"The Soviet Union's deployment of a large phased-array radar near Krasnoyarsk constitutes a significant violation of a central element of the ABM treaty," it said. "The Krasnoyarsk violation is very serious, particularly when it is recognized that the radar constitutes one of a network of such radars that have the inherent potential for attack assessment in support of ballistic missile defense.

"The United States has also made it clear that the continuing existence of the Krasnoyarsk radar makes it impossible to conclude any future arms agreements in the START or defense and space areas," it said.

The statement apparently was cleared by or came from Washington.

Mikhail Gorbachev ordered work stopped last year at Krasnoyarsk despite his contention that the radar is for tracking satellites and not part of an ABM project.

Gorbachev offers dismantling of the facility if Washington, as part of a strategic arms agreement, accepts a parallel accord limiting space defense systems.