President Reagan is to announce by June 10 whether the United States will continue to observe the unratified SALT II treaty.

There were indications yesterday that he will neither completely abandon the limits nor fully comply with them in the months ahead.

Reagan's commitment to report his decision on the controversial issue to Congress by June 10 -- and a general description of the factors he is considering -- were contained in a letter sent to Capitol Hill yesterday from national security affairs adviser Robert C. McFarlane.

A law passed last year required that Reagan report on the issue by today, but McFarlane said deliberations in the administration forced a brief delay.

White House spokesman Robert Sims said Reagan plans to present a definite decision when he makes his report, not just a listing of possible options.

Earlier in the week the White House had suggested that such a limited report was possible.

McFarlane's letter defined the administration's policy as one of "not undercutting existing strategic arms agreements so long as the Soviet Union exercises equal restraint."

Sims said the basic questions to be considered are "whether the Soviets are showing restraint and, if not, what action is it appropriate for us to take."

Virtually all elements of the administration are agreed that the Soviet Union is not fully complying with the SALT II limits, but there are differences about the degree and seriousness of Soviet noncompliance.

Guarded comments by administration officials suggested that Reagan is moving toward a tit-for-tat policy, in which the United States will stop short of full compliance on grounds that the Soviets are doing the same.

The practical issue is what the administration will do when the latest Trident submarine begins its sea trials in a few months.

This deployment would place the U.S. multiple-warhead arsenal above the 1,200 missiles specified in the SALT II treaty, unless other U.S. missiles are taken out of service at the same time to compensate for the additions.

A National Security Council meeting on the issue is scheduled for Monday.

After that, according to McFarlane, Secretary of State George P. Shultz will "consult with our allies" at a meeting of the NATO foreign ministers being held Wednesday and Thursdayin Lisbon