Ronald Reagan named his first eight Cabinet selections yesterday, including heads of the Treasury, Defense and Justice departments, and said that the men he picked increase his confidence "that Cabinet government can and will work."

The president-elect chose not to appear with the men who will help him govern, but the eight paraded single-file onto a stage in a Mayflower Hotel ballroom to have their names called by spokesman Jim Brady, be photographed and answer reporters' questions.

Reagan did not name anyone to the senior Cabinet post, secretary of state. He reportedly wants Alexander M. Haig Jr. for the post, but the nomination is being held up by fears that Haig's role in the Nixon White House might provoke controversial Senate confirmation hearings damaging to the administration in its first weeks in power.

Sen. Howard H. Baker Jr. (Tenn.), who will be the majority leader in the Republican-controlled Congress that convenes in January, gave Haig's candidacy an apparent boost yesterday. Baker said "Haig did nothing improper" in the Nixon years and could be confirmed. Baker added that he believes Reagan has decided to nominate Haig.

The eight nominees announced yesterday:

Donald T. Regan, chairman of the brokerage house Merrill Lynch and Co. Inc., to be treasury secretary.

Casper W. Weinberger, former secretary of health, education and welfare and director of the Office of Management and Budget, to be defense secretary.

William French Smith, Reagan's personal lawyer and financial adviser who is a senior partner with the Los Angeles law firm of Gibson, Dunn & Crutcher, to be attorney general.

Malcolm Baldrige, a Connecticut businessman who is chairman of Scovill Inc., to be secretary of commerce.

Sen. Richard S. Schweiker (R-Pa.), who had not sought reelection, to be secretary of health and human services.

Andrew (Drew) L. Lewis Jr., deputy chairman of the Republican National Committee, to be secretary of transportation.

Rep. David A. Stockman (R-Mich.), a Reagan economics adviser during the campaign, to be director of the Office of Management and Budget.

William J. Casey, Reagan's 1980 campaign chairman, to be director of the Central Intelligence Agency.

Together they are a mainstream Republican group, a Cabinet nucleus that will not alarm liberal GOP members although it may somewhat disappoint extreme conservatives who hope that a Reagan presidency will be strikingly different from previous Republican administrations.

As the eight white males in dark business suits appeared on the ballroom stage , they looked a little like a singing group without its choirmaster, but Reagan decided that his presence would detract from his nominees' first moment in the spotlight, spokesman Brady said.

"He feels this is their day. It's their show," Brady said.

The nominees did not seem to enjoy the show much. Weinberger was the first to make clear that he thought it inappropriate to give answers of substance to any questions before answering the questions of the Senate committees that will vote on confirming the Cabinet members, but all of the nominees spent much of the question-and-answer session orally ducking.

Smith answered several questions -- including ones concerning civil rights and Abscam -- by saying that he needed to do a lot of studying. "It's going to take a lot of learning before I can come to any conclusions," said the man who has been one of Reagan's closest political and financial advisers for years.

Smith was confident, however, that his personal relationship with Reagan would not lead to any abuses. "The question is the basic integrity of the individuals involved and, I think, there you will not be disappointed," he told a questioner.

Reagan's first eight nominees are a politically cohesive group. All worked for the Reagan campaign in one way or another.

Their average age is 56 despite the inclusion of the 34-year-old Stockman. Casey, 67, is the oldest; of the others, only Stockman and Lewis, 49, are under 50.

All had been reported as prospective Cabinet choices in speculative press reports that had been surfacing one name or another since shortly after Reagan's Nov. 4 election victory.

Baker has said he would like confirmation hearings to be held between Jan. 5 and Jan. 19 so that the full Senate can be prepared to vote on the nominees as soon as possible after Reagan's Jan. 20 inauguration.

Most of the questions put to the Cabinet nominees yesterday concerned economic policy.

Stockman was asked about cuts in the 1981 budget. He replied that the Reagan planners are "at a very preliminary state," but that there is "no indication we would back off" the 2 percent cut Reagan pledged in his campaign.

"Let's face it, inflation is the No. 1 problem facing the nation today," Regan said. He added that the Reagan team would have to devise an anti-inflation package including budget cuts and tax cuts. Regan ducked a question whether, as treasury secretary, he would be the administration's chief economic spokesman.

Schweiker was asked about controlling health care costs. "As a confirmed two-mile-a-day jogger," he replied, he will emphasize exercise and nutrition as ways to prevent disease.

He added that any budget cuts would be "in the area of fraud and abuse."

"I'm sure we're going to serve the needy people of this country," he said.

One area where Smith was willing to indicate his thinking was on conflict-of-interest laws and regulations. "I think there is much that is required that is unnecessary," he said of the requirements that Reagan advisers have said have delayed and complicated their efforts to form a Cabinet.

"They have gone through the most exhaustive and thorough scrutiny of any Cabinet nominees and they have given up rewarding careers to serve the American people in our joint undertaking," Reagan said in the three-paragraph statement that was distributed to reporters just before the eight Cabinet nominees entered the Mayflower ballroom.

Smith told a questioner she would have to decide for herself whether the Cabinet choices showed "balance" in the absence to date of female or minority members. Reagan had been reported to be looking for geographic balance. Two of the nominees, Smith and Weinberger, are Californians; Stockman comes from Michigan; the other five are from New York, Pennsylvania and Connecticut.

Reagan's incomplete Cabinet is surely the first to include two members of the small, 2,500-member Central Schwenkfelder Church, a German Protestant denomination to which Schweiker and Lewis belong.

All of the nominees except Stockman have extensive business experience.