WASHINGTON (AP) _ President Reagan and his National Security Council considered but reached no decision Monday on whether the United States will continue to abide by the unratified SALT II treaty.

A decision by Reagan is not expected until at least the end of the week, said one official, who demanded anonymity. The president gave no hint about what he intends to do about the treaty, the official said.

White House spokesman Larry Speakes said only that Reagan ''took under advice'' a review of the pact that had been made by his foreign affairs staff. The strategic arms limitation treaty expires Dec. 31.

The Reagan administration is reviewing its promise to abide by the treaty because its voluntary limits will be breached this fall when the newest Trident submarine begins sea trials. The Alaska, carrying 24 intercontinental missiles, will put the United States above the 1,200 limit for such weapons specified in the treaty.

The pact was negotiated under the Carter administration but was never ratified.

Speakes said a decision from Reagan is not expected until after Secretary of State George P. Shultz returns from consulting with the NATO allies in Europe later this week.

''We anticipate sending a letter (to Congress) by June 10 that will contain the president's decision on that subject,'' Speakes said.

Before the security council gathered, published reports said Shultz and Defense Secretary Caspar Weinberger were deeply divided over the timing of the president's decision with its far-reaching consequences.

Shultz is said to favor delaying a decision, while Weinberger is said to favor Reagan making the announcement that he will allow the pact to expire.

Speakes, however, refused to be drawn into a discussion about the reported feud and about the meeting itself.

Shultz will meet Thursday and Friday with the NATO foreign ministers in Portugal and their views will be taken into consideration, said the official who insisted on anonymity.

Reagan was scheduled to report to Congress June 1 on his policy toward the SALT pact and other arms limitation treaties, but the administration delayed sending the report because of its deliberations.

The administration and the Soviet Union have stated they would comply with the pact as long as the other side agreed to do the same, despite its never having been ratified by the Senate.

The Reagan administration, however, has accused the Soviet Union of violating the terms of the treaty by developing new missiles in excess of treaty limits.

White House deputy press secretary Robert Sims said the meeting left Reagan with a ''full range of options'' to take.

Speakes said the president still has the option of waiting until the Alaska goes to sea trials to make a decision, but he added that Reagan also ''could make a decision this week or next.''

Meanwhile, Senate Democratic leader Robert C. Byrd of West Virginia said he expects there is a great deal of support among Democratic legislators for not undercutting SALT II.

''As long as we do observe the constraints of SALT II, I think we have less to lose than do the Soviets,'' Byrd said. ''I think that as long as they are observing the SALT II restraints it probably means we will be required to dismantle fewer systems than they.''

''If we were to elect to throw SALT aside, it would give the Soviets a great propaganda weapon in Europe and I think it would undercut our efforts in Geneva'' at the US-Soviet arms control talks, Byrd said.

A number of varying amendments on the SALT II situation are due for consideration in the Senate shortly. Byrd and Republican leader Robert Dole of Kansas said they may be postponed until after Reagan announces his decision.

Byrd said he believes a decision to extend the SALT II limits should be for one year only to provide the opportunity for periodic reviews.

Reagan met later in the day with David Owen, leader of the British Social Democratic Party. Owen said he told Reagan ''that it is extremely important that you keep within the SALT limits'' and that the Alaska be drydocked rather than allowed to exceed the pact's limitations.

The British leader said that if Reagan gives up abiding by the treaty, the reaction among the European allies ''would be a very damaging'' for their ''faith in his seriousness in arms control.''