Reagan Decides Not to Scrap SALT : But Warns Soviets; Poseidon Submarine to Be Dismantled : U.S. to Abide by SALT II, Reagan Says

President Reagan, once a harsh critic of the SALT II treaty and other arms control measures, told Congress today that the United States will adhere to the unratified treaty and warned the Soviet Union to correct its violations of the accord.

“The United States has fully kept its part of the bargain; however, the Soviets have not,” Reagan said in a statement.

To keep the United States under the limit of multiple-warhead missiles allowed by the accord, Reagan said, he intends to dismantle a Poseidon submarine when a new Trident submarine puts to sea this fall.

But national security adviser Robert C. McFarlane, who read Reagan’s statement to reporters, said the United States may rebuild and reconfigure the Poseidon for use as a training vessel “or for some other purpose”--as he said the Soviets have done in at least one case.

McFarlane said the Soviets’ use of a former Yankee-class missile submarine as a new cruise missile launcher “departs from the spirit, if not the letter” of the SALT II treaty.

He said the United States retains the right to take a similar step as part of the “appropriate and proportionate responses” it is reserving in response to Soviet violations of the arms control pact.

SALT II, which Reagan condemned before winning the presidency as “fatally flawed,” is due to expire at the end of the year.

Reagan, who had been considering recommendations that he scrap the unratified treaty, said in the statement, “I am prepared to go the extra mile” in search of some framework for “truly mutual restraint” by the two superpowers.

“The United States will continue to refrain from undercutting existing strategic arms agreements to the extent that the Soviet Union exercises comparable restraints and provided that the Soviet Union actively pursues arms-reduction agreements in the currently on-going nuclear and space arms talks in Geneva,” Reagan said.

Reiterating his charge that the Soviets have tested a second new intercontinental ballistic missile in violation of SALT II’s one-missile limit, the President said the United States “reserves the right” to test the proposed single-warhead missile known as Midgetman “in an appropriate manner at the appropriate time.”

The Midgetman is not expected to be ready for testing for at least two years.

Also today, Reagan urged Soviet leader Mikhail S. Gorbachev to correct “extremely serious” violations of the unratified accord, an Administration official said today.

In a letter to the Soviet leader, Reagan explained his decision to adhere to the unratified treaty as designed to leave the door open to concluding a more up-to-date accord by U.S. and Soviet negotiators in Geneva. Those talks, which opened in March after a 15-month suspension, apparently have produced virtually no progress.

In the Senate, Republican and Democratic leaders hailed the announcement.