Despite President Reagan's statements that his administration is moving to exceed the limits of the unratified SALT II treaty later this year, the timing of such an event is uncertain.

The Air Force and the Navy are keeping options open that would permit the United States to continue to remain in technical compliance with the agreement, according to Pentagon officials.

Reagan threatened to exceed the SALT II limits later this year by building more B52 bombers capable of carrying air-launched cruise missiles than permitted by the pact.

But the president left open the possibility that he could make other reductions that would keep the United States in technical compliance by saying he would "take . . . into account" any "constructive steps" taken by the Soviets to satisfy U.S. concerns about their alleged violations of the SALT II agreement.

"I wouldn't be surprised if they changed direction [on the B52 modification program]," one Pentagon officer associated with the cruise missile program said of his civilian superiors yesterday. "I read the papers and see opposition growing to exceeding the limit," he said.

The Air Force cannot say for certain when the United States will exceed the SALT II limit of 1,320 multiple-warhead systems by producing its 131st B52H equipped to carry cruise missiles, a Pentagon spokesman said yesterday.

"We are not sure when that number will come up," the spokesman said, noting that by counting two cruise missile-capable test B1B aircraft and one test B52H, the total may be reached in late November or December. Previously, the Strategic Air Command has not been counting those three test planes against the SALT II limit. The tally can also be affected by accidents. A cruise missile-carrying B52G crashed in October 1984, reducing the number of counted bombers by one.

Defense Secretary Caspar W. Weinberger reflected the Pentagon's confusion on the timing of new deployments by telling journalists the day after the president's decision that he thought it would be "August or September, somewhere in there" when the SALT II limit would be breached. A day later he changed his guess to later in the year.

The date is important for diplomatic and political reasons. The Soviet Union has announced it will not take any new military steps in response to Reagan's abandoning of the SALT II pact until after the United States actually goes over the limit. On the political front, the president will have to review his decision in the September-October period, in the midst of a key congressional election that could shift control of the Senate to the Democrats, and possibly on the eve of a summit with Soviet leader Mikhail Gorbachev.

At one point, the Air Force was prepared to keep the bombers within the original SALT II limits by introducing basic wiring in B52s to enable them to be modified quickly for use on cruise missile carriers without completing the conversion.

In a related development, Navy officials said that their service was far from certain it would keep two 20-year-old Poseidon submarines, scheduled for overhaul next year, as ballistic missile-firing boats once they are refurbished and refueled. "We have not made provision for the four crews that would be necessary to operate those boats" as missile-carrying submarines, one Navy officer said.

Instead, he said, the service is studying the possibility of using the refurbished submarines as transports for special forces or even cruise missile carriers.

If these submarines are not returned to duty with their intercontinental missiles, they will no longer count against the SALT II limits.

Taking them out of service in this way may restore technical compliance with the treaty for at least another 1 1/2 years, even if new deployments of cruise missile-carrying bombers continue on schedule.