President Carter will authorize the National Archives to begin a search for specific presidential tape recordings and documents sought by Senate Democrats for use in the confirmation hearings of secretary of state-designate Alexander M. Haig Jr., White House press secretary Jody Powell said yesterday.

While Powell, in an interview on "Face the Nation" (CBS, WDVM), stressed that the White House will still allow former presidents Richard M. Nixon and Gerald R. Ford to invoke executive privilege, the president's action apparently overrules the decision of Carter's national security affairs adviser, Zbigniew Brzezinski, to decline the senators' request.

Brzezinski had turned aside an earlier appeal by Sen. Claiborne Pell (D-R.I.), who will be the ranking minority member of the Senate Foreign Relations Committee when the new Congress convenes today. Brzezinski wrote Pell that a formal request from the full committee, which has a Republican majority in the new Congress, would be necessary before the White House would begin processing the materials sought.

Brzezinski said in an interview Saturday, "We're not going to be partners to some indiscriminate witch hunt."

A White House spokeman yesterday declined to say that Brzezinski has been overruled and emphasized that the Senate may never get any materials if Nixon or Ford assert executive privilege.

Nevertheless, Carter's cooperation may force the Senate to delay concluding the hearings, at least until the requested materials have been located and analyzed and until any assertions of executive privilege have been made, according to Senate sources.

Pell refused to comment on Powell's statement until he had seen a transcript of the program. He said, however, that he was "delighted" at the apparent White House shift in position.

Carter has not yet forwarded the second Pell request to archivist Robert G. Warner, the White House spokesman said, but will forward it "early this week."

According to a source at the archives, even a specific request would require a minimum of a week to gather the materials in one place before sorting out individual documents relevant to the request.

Committee staff members say they expect the availability of the new material will put pressure on Pell to ask the Republicans to delay the conclusion of the hearings, which are scheduled to begin Friday.

"Otherwise, [the Democrats] have got no ground to complain that Haig was railroaded through by the Republicans," one staff member said.

"We'll cross that bridge when we come to it," Pell said in a telephone interview yesterday. Pell said he still intended to cooperate with incoming committee chairman Charles Percy (R-Ill.) to get the hearings started next Friday and "to close by Inauguration Day."

When Pell originally consulted with Senate lawyers about access to Nixon's tapes and documents, he was told that one of the options was that Nixon could release them. Pell made a request to the former president, but Nixon still has a case pending in the U.S. Court of Appeals to prevent release of his tapes as an invasion of his privacy, and his cooperation was considered unlikely.

Pell was told that Carter, as the current president, could release materials "necessary for the ongoing operation of the executive branch." Since a secretary of state will certainly be necessary to Reagan's operation of the executive branch, Pell decided also to exercise that option.

If Reagan were president, he would not oppose the release of any tapes or documents relating to Haig, James A. Baker III, Reagan's designated chief of staff, told reporters at a breakfast meeting last month. However, since Reagan will not be sworn in until the hearings are scheduled to end, Pell directed his request to Carter. Carter reportedly has been advised by White House legal counsel that he must allow each of the former presidents an opportunity to assert executive privilege before releasing any materials.

Pell sought from Nixon any tapes and documents relevant to Haig's involvement in wiretapping, other controversial foreign policy advice, Nixon's Watergate defense and pardon.

At Brzezinski's insistence, Pell refined his initial, more general request to the White House, specifying some materials by time and place.

The White House and Pell's office refused to make public Pell's second request.

"We don't want to tip off [Haig] to the specific areas in which he will be probed," one Senate staff member said.