Sen. Henry M. Jackson (D-Wash.) yesterday vowed to fight in the Senate to send the strategic arms limitation treaty (SALT II) back to the bargaining table, with instructions to U.S. negotiators to seek "an equal agreement" that cuts the size of the Soviet Union's missile arsenal.

Jackson, the Senate's leading SALT II opponent, said he would move to recommit the treaty, "to go back to the negotiations with the Russians, with instructions to achieve what Congress has previously required by statute - that there be an equal agreement."

The SALT II treaty is to be signed today by President Carter and Soviet President Leonid I. Brezhnev at a meeting in Vienna. Carter said it would be "very difficult" to reopen negotiations "because why should a president of the Soviet Union want to negotiate with the president of the United States if ultimate approval by the Senate of a carefully balanced treaty was extremely doubtful?"

Speaking on "Issues and Answers" (ABC, WJLA), Jackson said that Carter has a "mandate" from the Senate, after the 1972 SALT I treaty signed by President Nixon, to seek a second SALT pace that left the United States "equal" with the Soviets in strategic military strength. "The administration had a mandate and they ignored it," Jackson said.

Jackson also said the president made a "serious mistake" in not involving the bipartisan Senate leadership more closely in the negotiations.

Jackson, chairman of the arms control subcommittee, has made his opposition to SALT II known before, most recently in a speech in which he called the agreement "appeasement in its purest form." Yesterday, however, Jackson revealed his strategy for attempting to secure a SALT treaty more to his liking.

Other SALT II opponents and undecided senators have indicated they would propose substantive changes in the treaty. Jackson, however, said he wants the entire package renegotiatiated, "with instructions to make specific amendments."

"The Constitution says we [the Senate] give our advice - that's part of it," Jackson said. "And before we give our consent, there are conditions that have to be met."

Jackson also defended and elaborated on his earlier charge that the Carter administration had followed a policy of "appeasement" with the Soviets. "The period of the Ford/Kissinger years was not appeasement," he said. "I would point out that the agreement they were working on did not go the direction this administration has traveled in connection with SALT.

"I would point out that since the president has taken over in 1977, he has moved from a hard bargaining line with the Russians and, on each and every meeting after the first meeting, concessions were made of substantial nature, and that is appeasement."

Jackson said in the renegotiations he seeks, the United States must get and agreement that cuts back the number of Soviet Intercontinental ballistic missiles, not slowing down the arms race.

"What we'll want to do [in renegotiations] is to zero in on two things - that there be equality, that there be verifiability," jackson said. "I would like to see basically a cutback in those huge missiles . . . That should be one of the primary goals. But there must be a recognition of equality." CAPTION: Picture, Sen. Henry M. Jackson