Key elements of an intended American-Soviet compromise on a partial nuclear arms accord were guardedly disclosed yesterday by President Carter.

"Some constraints" on developing American long-range cruise missiles are contemplated, the President acknowledged, along with "some constraints on the [Soviet] Backfire bomber." Cruise missiles are the greater American technological innovation.

The President revealed that the United States also seeks some offsetting limitation on "vey heavy missiles of the Soviets which causes great concern." He said these would be "temporary solutions," for two or three years, "giving us more bargining time" for deeper arms cuts. [TEXT OMITTED FROM SOURCE] included in a protocol to a U.S. Soviet.

These potential tradeoffs would be included in a protocol to a U.S. Soviet nuclear limits set at Vladivostok in 1974, which the Russians seek to confirm.

The United States hopes, Carter added, to obtain "significant reductions below the Vladivostok levels" set by Soviet leader Leonid I. Brezhnev and former President Ford.

In early 1976, former Secretary of State Henry A. Kissinger was negotiating reductions of up to 10 per cent in the Vladivostok arms ceiling of 2,400 strategic missile launchers and bombers. Kissinger was blocked by opposition to his intended terms for a cruise missile-Backfire compromise, with the Pentagon and Sen. Henry M. Jackson (D-Wash.) leading the opposition.

Secretary of State Cyrus R. Vance yesterday carried the Carter administration's ideas for a compromise to an unusual closed meeting of the Senate Armed Services arms control subcommittee, headed by Jackson and attended by Democratic and Republican leaders of the Senate.

Jackson said after a two-hour closed session with Vance that a break-through agreement has been achieved with the Carter administration on sharing information about the Strategic Arms Limitation Talks (SALT).

"We've had, I think, a rather historic meeting," Jackson said, "in that the leadership on both sides of the aisle, Republican and Democratic, participated in the hearing today which will continue to be the course of action we will be following."

The Carter administration is extremely sensitive to the need for a two-thirds vote in the Senate to approve a new SALT accord. Jackson is the potential leading challenger, as he was of Kissinger, and the President has intensively solicited his support in recent weeks.

Participants declined to discuss any details of the negotiations, which members of the Senate now hope to influence as the secret bargaining proceeds with the Soviet Union.

Under a negotiating format set in Geneva last week by Vance and Soviet Foreign Minister Andrei A. Gromyko, an agreement on a nuclear treaty until 1985 and a three-year protocol, would be accompanied by a commitment to negotiate promptly deeper nuclear arms cuts, the basic Carter goal.

Carter yesterday differentiated this target as "drastic substantial reductions" in nuclear arsenals.

He said there was "a great deal of harmony" in the Vance-Gromyko talks in Geneva last week, compared to Moscow - where each side flatly rejected the other's proposals. The President agreed "it was an upbeat meeting as described by Secretary Vance."

Asked by a newsman to reconcile that with Gromyko's "downbeat words" at Geneva last Saturday, the President said there are "substantial remaining differences" and "when you emphasize the differences that still remain . . . there is cause for some concern."

Gromyko left Geneva charging that the United States was still seeking "unilateral advantage." One of Gromyko's criticisms evidently was of the U.S. proposal revealed by Carter yesterday for including some limitation on Soviet "very heavy missiles" for a three-year period as a step toward a broader agreement. The long-range U.S. plan, which Gromyko denounced in Moscow in March, calls for scraping more than half of these largest Soviet missiles.

The President yesterday described the Geneva discussions last week as "an exploratory meeting" in which Soviet willingness "to assess our positions and to modify their own, I think was reciprocated by us . . . "

Senate Foreign Relations Committee chairman John J. Sparkman (D-Ala.), after hearing Vance testify in closed session on Wednesday, said, "There was a bit of horse-trading in Geneva and the stage has been set for further horse-trading."