A series of compromises and accomodations acceptable both to the Department of Defense and the Soviet Union have in the past week brought the two superpowers to the verge of a final agreement on a new strategic arms limitation treaty (SALT), according to officials who are familiar with the details.

As presently taking form, the SALT II agreemens will permit each nation to invest billions of dollars in new weapons systems during the seven year duration of the pact. A major selling point with the Pentagon is an explicit statement which is to be made by President Carter that the United States reserves the right to build a new, advanced penetrating bomber system comparable to the Soviet "Backfire." This is being taken as a clear signal that the Carter administration will approve a follow-on version of the FB111 bomber.

Another new element in the politics of SALT is the forthcoming resignation of Paul C. Warnke as chief U.S. arms control negotiator, according to informed officials.

A controversial figure since being named to the job. Warnke will bow out after the agreements are worked out with the Soviet Union, probably late this month, and return to private law practice. Part of the planned arrangement is that he will continue to be available to testify in Congress on the agreements he helped to negotiate.

Warnke said yesterday it had been "no secret" that he could stay in the job for only a limited time because of personal commitments. "We don't have a date picked" for his departure at present, he said.

Due to the compromises recently made or set in motion, administration officials are increasingly confident that the essential elements of the SALT agreements will be worked out during the visit to Moscow by Secretary of State Cyrus R. Vance scheduled for the second half of this month. If this is done, the treaty would be ready for signature by Carter and Soviet leader Leonid I. Brezhnev at a summit meeting which may take place in the United States about Dec. 1.

Administration officials caution that the apparent SALT deal, all but worked out during the recent visit of Andrei A. Gromyko, the Soviet foreign minister could still come undone if Gromyko's Politburo colleagues disapprove of the negotiating steps he took here. There are also several unresolved issues that could hold up the process. But on balance, U.S. officials anticipate successful completion of the negotiations.

As described by informed sources, the U.S. Soviet compromise that will overcome the remaining obstacles to a new treaty includes:

On the much-disputed Soviet Backfire bomber, the Soviet Union will provide assurance that it will not be deployed in a way that threatens the United States. The United States for its part will declare that it retains the option of producing a new penetrating bomber of a similar type, which is expected to be the successor to the swing-wing FB111. Neither system would be counted against the SALT II limit on strategic nuclear delivery systems.

The Soviets insist that the Backfire (a NATO designation is an intermediate-range plane that would not be used as a long-range strategic bomber against the United States, but the Pentagon is equally insistent that the plane could reach American shores from Soviet bases. The Pentagon does acknowledge, however, that the weapon is primarily useful for intermediate-range missions.

Each side would be permitted to flight test one "new type" of landbased intercontinental ballistic missile. For the United States this would likely be the planned MX missile, which could eventually be deployed as a mobile missile, and the Soviets are expected to develop a new single-warhead missile to replace the SS11 that is a mainstay of its arsenal.

Some officials maintain that the agreed-upon restrictions on new types of missiles will prevent the Soviets from fully developing two of the three missiles they have been working on, but this could depend on final treaty language that is not yet drafted.

Deployment of these new missiles will be allowed only after the expiration of a protocol that will be part of the new SALT pact. The protocol will remain in force for several years - its duration remains to be negotiated.

No limit on "new types" of submarine-launched ballistic missiles would be imposed, making it possible for the United States to test and deploy its Trident I missile and even a Trident II, which is in a planning stage. The Soviets would also be allowed to produce new submarine-based missiles, encouraging them to shift the weight of their nuclear power from land to sea, which is felt to be more stable.

Warnke's decision to leave his post as director of the Arms Control and Disarmament Agency follows months of uncertainty about his role in what is expected to be a bitter and close fight for approval of a new SALT pact in the Senate.

Hardline critics of the SALT negotiations have made Warnke into a whipping boy, accusing him of being too eager to reach agreements that might not be in America's best interests. Warnke has called these charges ridiculous.

Officials privy to Warnke's recent decision to step down later this fall insisted yesterday that he had not been forced out, but decided to go voluntarily. These officials also said they expected some participants in the SALT debate to look for more conspiratorial explanations for Warnke's departure.

Warnke's role had been a matter of deep concern and intense discussion at the highest levels of the Carter administration. According to one school of thought, it would be a grave mistake to let Warnke leave office before the Senate had acted on the SALT pacts, because Senate hardliners would use his departure as an implicit admission that the administration lost confidence in him.

That would not help the White House sell a SALT agreement which Warnke had been instrumental in negotiating, according to officials who held this view. Moreover, they argued, it wouldn't be fair, since they said Warnke had been a tough and effective negotiator.

Other senior officials felt Warnke had alienated too many senators with an aloof manner that some feel is condescending, and had become too much of a symbol for the hardliners, and so had to leave.

Warnke was aware of the debate that surrounded his future role. He also knew that a lucrative Washington law practice in the firm headed by Clark Clifford, the former secretary of defense, awaited him whenever he chose to resume it. Warnke noted yesterday that he has three children in college and a fourth in graduate school.