The Carter administration switched the target of its SALT diplomacy last week from Moscow to Capitol Hill, and gained a congressional nod to continue the search for a compromise nuclear arms accord.

Throughout the intricate bargaining ahead, the administration now appears locked-in to continuing negotiation on both fronts.

President Carter disclosed over the weekend an accelerated pace of American-Soviet nuclear strategic arms limitation talks. He said Secretary of State Cyrus R. Vance and Soviet Foreign Minister Andrei A. Gromyko will meet twice before mid-September to work toward a nuclear agreement.

When Vance and Gromyko finished their last meeting at Geneva on May 21 Vance referred to only one projected meeting. The current temporary U.S. Soviet limitation on offensive strategic nuclear weapons expires Oct. 3. The Carter administration repeatedly has said will not be hurries by "any deadline into a precipitous accord - and that if there is no new agreement by Oct. 3 - the deadline can be extended, formally or tacitly.

Speeding up the SALT talks makes senators who are demanding hard bargaining with the Russians more wary of compromise efforts.

No one officially describes last week's private exchanges between the administration and potential Senate critics of a new nuclear arms pact as "a negotiation."

And yet they were the political counterpart of the "framework for negotiations" reported in Geneva by Vance and Gromyko. Carter may have invested as much personal effort in clearing the Capitol Hill path for continuance of the new arms talks as he did for the actual Geneva negotiations.

Each of them carries almost equal priority for administration strategists. And both are tenuous.

A closed meeting between Vance and about a dozen influential senators last Thursday was described by Sen. Henry M. Jackson (D-Wash.) as "rather historic."

An administration agreement to share information as the SALT negotiations proceed, sanctified by the presence of Senate Democratic and Republican leaders, Jackson said, was a breakthrough toward "a truly non-partisan or bipartisan foreign policy," not seen since the post-World War II era.

Skeptics inside and outside the administration, however, regard the current situation as more of a wary political truce than a peace settlement.

Some administration strategists are delighted that Jackson put such a high gloss on the information-sharing arrangements he reached with the executive branch.

Jackson "wants to be seen as a statesman - not a loner - in a Democratic administration," said one insiders. "That is fine with us."

Vance said after the meeting Thursday with Jackson's Senate Armed Services Arms Control Subcommittee and Senate leaders:

"It is very helpful to me and to the administration to have the opportunity to share views on how we should proceed in these very complicated areas."

Beneath the new air of harmony, however, neither side is abandoning its view of what should be in or out of a new nuclear treaty with the Soviet Union.

"There are differences between Jackson and the administration already," one official acknowledged privately, "and they are never going to be reconciled entirely." Jackson agrees "I have differences."

Nor, administration officials say, are Jackson and fellow advocates of hard bargaining with the Russians being given "a veto" over the administration's bargaining terms.

Jackson and other senators will be "cut in" on the administration's strategy, so that they can "express their views," it is said.

However, administration sources say, they do not intend to be caught in a position where the information they share can be used "to build a backfire" against official strategy. That is the nub of the problem; the constant dilemma of almost every administration.

When Vance's predecessor, Henry A. Kissinger, dominated the scene in the Nixon years; he "cut out" internal opponents in SALT negotiations by extraordinarily tight control of information, including "back channels" behind the official U.S. negotiators.

Kissinger counted on "his own charisma," as one participant put it, to push the original 1972 SALT nuclear accords through the Senate. Jackson, leading the challenge to Kissinger, dominated the floor debate in which the pro-treaty forces were led by Sen. J. W. Fulbright (D-Ark.), then chairman of the Senate Foreign Relations Committee. The treaty was approved. But Jackson not only left his mark on the legislation. With expertise on nuclear, hardware, he also carved out an enduring position as the strongest power broker in Congress on SALT II negotiations.

In early 1976, the joint opposition of Pentagon military leaders, Jackson, and allies in the Arms Control and Disarmament Agency, blocked Kissinger and President Ford in the SALT II negotiations.

Carter took office sensitized to the problem of "internal negotiations" on SALT.

Raymond Garthoff, a senior Foreign Service officer who was the U.S. delegation's executive officer in the first SALT negotiaions, recently wrote in Harvard University's International Security quarterly:

"Challenging as is the task of negotiating with the Russians, our greatest difficulties in doing so have arisen from the attendant burden of continual negotiating and maneuvering among various elements within the American government."

The Senate's power to sanction or thwart a treaty, granting or withholding the necessary two-thirds vote, was underscored for the Carter administration in early March by a salvo cross its bow.

Jackson led a symbolic test of strength against Carter's official chief negotiator on SALT, as "too soft." The advocates of sterner negotiations displayed potential capacity to produce "a blocking third-plus-one" on any SALT treaty by marshaling 40 opposition votes, although the President's nominee, Paul C. Warnke, received a majority vote of 58 for his confirmation in that post.

The White House got the message. The SALT proposal that emerged from the White House later in March was tough enough for hawks to welcome, yet also comprehensive enough for doves to embrace - as an opening bid. The problem was the Russians; they rejected it out of hand in Moscow.

Then came inevitable probing on both sides for a compromise, culminating in the "framework agreement" in Geneva, an agenda.

President Carter did much of the groundwork himself to gain the acquiescence of Congress, assuring Jackson and others there were no binding commitments in Geneva on substance.

On the day the Vance-Gromyko talks began in Geneva, the President met with Senate leaders, ranking members of the Senate Foreign relations and Armed Services committees, and other senators believed to need early courting for the distant voting on a SALT treaty.

The next day, Jackson was back at the White House, with his wife and their two children, for a dinner with the President and his family. Jackson was at the White House again last Tuesday night, at the official dinner for Saudi Arabia's Crown Prince Fahd.

Many Senate doves, eager for a new SaLT accord, welcomed the burgeoning Jackson rapprochement with the White House on SALT.

Jackson was being "very helpful" to the President, Sen. Hubert H. Humphrey (D-Minn) said encouragingly, the day the Geneva talks opened. Some people, Humphrey said, regarded Jackson as "a hard-liner" on SALT; why in fact, Humphrey said, Jackson was "a hard-thinker" on SALT.

Jackson was looming as the Senate spokesman on SALT. Not so, protested several Senate doves; but they did their talking in private. No one was inclined to antagonize Jackson.

Last Thursday, Jackson reached out for clear primacy, presiding over the meeting attended by Senate leaders and others from outside his arms control subcommittee.

?This will continue to be the course of action that we will be following," Jackson announced afterward.

To reach "the kind of agreement that . . . will stabilize the situation in the world," Jackson said, "starts with an understanding of those who must approve the treaty on both sides of the aisle, and that's what's emerging here today."

Among participants were Senate Majority Leader Robert C. Byrd (W. Va.); Senate Minority Leader Howard H. Baker Jr. (Tenn.); Democratic Whip Alan Cranston (Calif.); Republican Whip Ted Stevens (Alaska); Senate Armed Services Committee Chairman John C. Stennis (D-Miss.); and, Jackson pointedly noted, Sen. Clifford P. Chase (R-N.J.), "the ranking minority member of the ForeignRelations Committee . . ."

Concern is now rising among Senate doves that Jackson is out to preempt the Senate field on SALT.

The Senate's Foreign Relations Committee chairman, 77-year-old John J. Sparkman (D-Ala.) is no challenger. The next-in-line on the dovish committee, Sen Frank Church (D-idaho), is sensitive to any loss of committee influence, especially on SALT. Several of that committee's younger members now are "boning up" on the complexities of nuclear weaponry, for the contest when a SALT treaty reaches the Senate.

Long before then, other Senate doves fear, the pressure for toughness with the Soviet Union, from Jackson and fellow hawks, on such issues as developing a full complement of American long-range cruise missiles, risks freexing-up a U. S. Soviet SALT compromise.

The Carter administration has disclaimed any "formalized arrangement" to give preference to the Jackson subcommittee formula as the prime vehicle for SALT consultation.

"It is up to the Senate itself to decide that," said one official. What the Carter administration wants is maximum support of both hawks and doves as it tries to thread its way past the Russians and Congress to a SALT accord.

But it is the Jackson challenge, the stronger of the two, that is receiving the major attention.