Soviet leader Mikhail Gorbachev today called on the United States to reaffirm "in a binding form" its commitment to the antiballistic missile treaty.

In a message to a group of American scientists, Gorbachev repeated Soviet charges that the U.S. strategic defense initiative (SDI) poses a threat to the treaty and to the entire process of arms control.

The ABM treaty, signed in 1972 and still in force, is considered by the Soviets to be the foundation of the arms control process and its most successful product.

In today's message, published by Tass, Gorbachev stated that the Soviet Union "unswervingly observes the spirit and the letter of that document of paramount importance."

"The Soviet Union is not developing attack space weapons or a large-scale ABM system," he said, arguing that the U.S. SDI "would invariably lead to the breakup of that document, the key link of the entire process of nuclear arms limitation."

The message was in reply to a proposal for a ban on space weapons made to both the Kremlin and the White House by the Union of Concerned Scientists.

The Soviets recently have stepped up their attacks on SDI, a space-based defense, saying that a continuing U.S. commitment to the program could jeopardize progress at the arms talks in Geneva.

The United States has argued that research is not banned by the ABM treaty, and has claimed that the Soviets are conducting similar research themselves.

Gorbachev's appeal for preserving the ABM treaty came one month after Marshal Sergei Akhromeyev, chief of the Soviet general staff, accused the United States of trying to tamper with the treaty.

In his message today, Gorbachev repeated Soviet proposals for a ban on a space attack system and a moratorium on antisatellite systems. He called on the United States to join the Soviets in scrapping any existing antisatellite systems, including those not yet tested.

The U.S. Air Force has said that its first test of an antisatellite system against a target was scheduled for this month. But the House has voted to ban U.S. tests as long as the Soviets do not conduct them and the issue is awaiting a resolution in Congress. The Pentagon has said the Soviet Union already has an operational antisatellite system against low-orbiting satellites.