The Joint Chiefs of Staff have sent a secret policy document to President Reagan that supports any SALT II decision he makes without disclosing that some of them favor adhering to the weapons limits in the agreement, according to Pentagon sources.

The chiefs carefully crafted the document in hopes of avoiding an open policy split with Reagan and keeping themselves out of the political storm they foresaw if the president abandoned the arms pact, sources said.

But House Armed Services Committee Chairman Les Aspin (D-Wis.) and other lawmakers are expected to drag them into the storm by demanding to know their personal views on the wisdom of abandoning the limits in SALT II. Aspin said he intends to summon the chiefs before his committee.

Several senators also are pressing to question the chiefs. But Senate Armed Services Committee Chairman Barry Goldwater (R-Ariz.) said in an interview that he has no intention of letting his committee be a forum for such cross-examination of military leaders, contending that what Reagan did on the SALT limits "is none of Congress' business."

Adm. William J. Crowe Jr., chairman of the Joint Chiefs, engineered the document sent to Reagan. Sources said it states that the chiefs' primary interest is to get new generations of strategic missiles, bombers and submarines deployed. The question of whether this can be done better inside or outside SALT II is a political call for the president, not the military, the document contends.

Under this approach, whether Reagan stuck with the weapons limit in SALT II or abandoned them, as he has done, the White House and the chiefs can say that the Joint Chiefs of Staff, the nation's highest military body, support the president's decision. An earlier group of chiefs supported the SALT II treaty, support that President Jimmy Carter considered essential but which was not enough to win Senate ratification.

The chiefs, in debating their position on SALT II, knew from frequent meetings with Defense Secretary Caspar W. Weinberger -- who usually meets with them as a group on Tuesday and Thursday and sees Chairman Crowe more frequently -- that he strongly opposed continuing to observe SALT II. Just as their predecessors felt heavy political pressure to support SALT II, today's chiefs felt pressure to oppose it, according to knowledgeable officials.

Also, according to sources, there was widespread agreement among the chiefs that the Soviet Union had been flagrantly violating SALT II by encrypting telemetry and deploying the SS25 blockbuster missile. They sympathized with the president's plight in which he would seem to tolerate such violations if he continued to observe the pact.

A counterargument in "the tank," the big room in the Pentagon where the chiefs deliberate, sources said, was that anything that limited how many nuclear warheads the Soviets targeted on the United States would ease the military's problems in countering them. The Soviets do scrap missiles to comply with the treaty. Without SALT II, these missiles would be available for "breakout," a sudden deployment of warheads, this argument went, sources said.

As for new strategic weapons, the chiefs agreed and told Reagan, sources said, that the Soviets in the near future are not likely to build them any faster without SALT II than with the limits being observed.

Under traditional procedure, the chiefs support presidential decisions in testifying before Congress. Only when they are asked for their personal opinions do they sometimes break ranks with the president. Lawmakers critical of Reagan's abandonment of SALT II have dug up past testimony of military leaders endorsing the treaty limits in hopes of drawing out the qualms of today's chiefs.

Such research, sources said, has revealed that in late March Gen. Larry D. Welch, then head of the Strategic Air Command and now Reagan's nominee to be Air Force chief of staff, told a secret session of the Senate Armed Services Committee's strategic and theater nuclear forces subcommittee that he thought it would be militarily advantageous to the United States to continue complying with the arms limits of SALT II.

At his confirmation hearing before the committee on Friday, Welch said the Soviets, in deploying the SS25 and encrypting its telemetry, had "not only violated the letter but the spirit of SALT II." No senator asked him if the violations had reversed his support of the treaty limits, however, a question he and other military leaders are expected to be asked in the coming weeks as the SALT II conflict between Reagan and Congress escalates.

A Pentagon official said that whatever personal concerns the chiefs may have about abandoning SALT II, Weinberger feels vindicated in advocating the scrapping of the treaty because the Soviets, since the president's decision, have put a new arms-control proposal on the table at Geneva.