The Senate voted 93 to 6 yesterday to confirm President Reagan's nomination of Alexander M. Haig Jr. as secretary of state, brushing aside a complaint from Minority Leader Robert C. Byrd (D-W.Va.) that Haig had left "unanswered questions . . . . regarding the abuse of power."

Haig, chief aide to President Nixon in the aftermath of Watergate and former commander of the North Atlantic Treaty Organization, was the second Reagan Cabinet nominee to win Senate confirmation. Caspar W. Weinberger was confirmed as secretary of defense within hours after Reagan's inauguration on Tuesday.

The Republican-controlled Senate, seeking to give Reagan as much of his Cabinet as possible this week, yesterday also unanimously approved Donald T. Regan as treasury secretary, Bill Brock as trade representative and Richard S. Schweiker as secretary of health and human services.

Despite five days of grueling hearings and a battle over subpoenas, Haig won confirmation with relative ease, drawing praise from many Democrats as well as Republicans for his hard-line foreign police views and mixed reviews for his role in the Nixon White House.

The negative votes came from five Democrats and one Republican: Byrd, Carl Levin (D-Mich.), Donald W. Riegle (D-Mich.), Paul S. Sarbanes (D-Md.), Paul E Tsongas (D-Mass.) and Lowell P. Weicker (R-Conn.).

Even some of these praised Haig's intelligence and skills, with Tsongas calling him an "extraordinary man . . . intelligent, tough, pragmatic." Their criticisms centered on what Sarbans, a member of the House Judiciary Committee when it voted to impeach Nixon, called "the use of power in our constitutional system and the judgement Gen. Haig will make in this regard."

Byrd tempered his criticism, noting that some of the "unanswered questions" were never asked but saying that Haig's record on uses and abuses of the power amounted to a "clouded" case for confirmation. "While I believe Gen. Haig has respect for the Constitution of the United States, I am afraid that he lacks a fundamental understanding of, and sensitivity to, the designated and distinct roles and responsibilities of the executive and legislative branches of our government," said Byrd.

Haig's strongest defense on the Watergate issue came from Sen. Barry Goldwater (R-Ariz.), whose praise of Haig and affirmative of confidence in Reagan administration foreign policy prospects brought an outburst of applause from the gallery.

Goldwater claimed that Haig was principally responsible for keeping Nixon from fighting impeachment to the end, adding that those who try to link Haig with Watergate-related abuses are "talking through a rather empty hat."

The bitterest criticism of Haig came from Weicker, who accused him of having "consistently chosen the lower road" and showing a "monumental contempt for both Congress and the individual rights and liberties of all Americans as enunciated in the Constitution of the United States."

But Haig also appeared to have some possible trouble for the future -- from Republican conservatives.

Sen. Jess Helms (R-N.C.) and 16 other conservative GOP senators have complained to Haig about some of his rumored choices for subsidiary positions in the State Department, including Democrats and Republican moderates who served under President Ford and then-Secretary of State Henry A. Kissinger.

"We're sending a message and it's being heard," said Helms, who opposed confirmation of Weinberger on Tuesday and is trying to hold up confirmation of Frank Carlucci as his deputy in order to assure choice of what Helms calls "knowledgeable detense experts" in other major Pentagon posts.

During debate on Haig, Senate Foreign Relations Committee Chairman Charles H. Percy (R-Ill.) indicated he may be having second thoughts about pursuing subpoenas for indexes of Nixon White House tapes involving Haig. Percy noted that the national archivist has accepted objections raised by Nixon's attorneys to access to the materials and said the committee will have to decide whether to go ahead with the subpoenas.