President-elect Bush said Friday he will unveil ideas for reducing the deficit to a special joint session of Congress after his inauguration.

And while expressing support for President Reagan's decision to back a 50 percent pay increase for members of Congress and other top federal officials, Bush said he may revisit the question when he is president."I don't know whether we can afford anything other than to get this deficit under control," he said.

Bush's transition office later announced Bush will nominate Lawrence S. Eagleburger as deputy secretary of state and has selected his national security adviser, Donald P. Gregg, as ambassador to South Korea.

Eagleburger is a Henry Kissinger protege who is currently president of Kissinger Associates, the consulting firm founded by the former secretary of state.

The Gregg nomination could spark controversy because of Gregg's role in the Iran-Contra affair while serving on Bush's vice presidential staff, which he joined in 1982 after retiring from the Central Intelligence Agency.

The transition office also announced a string of other appointments to top State Department posts and several prominent ambassadorships, including the nominations of Henry E. Catto, a former White House protocol chief, as ambassador to Great Britain, and Vernon A. Walters, the outgoing United Nations ambassador, as ambassador to West Germany.

There was no word from Bush on when he will fill his last two Cabinet-level vacancies, energy secretary and drug-czar, and aides said he still has not made up his mind.

Bush, fielding questions from reporters at the start of a meeting with small-business executives, also said the Iran-Contra prosecutor Lawrence Walsh "did the right thing" in moving to drop two key charges against Oliver North because of national security concerns.

"It's the proper suggestion. And I think he properly found that there are legitimate national security interests that need to be protected. . . . " said the vice president, who last week was subpoenaed by North's lawyers to testify in the case. "I think he did the right thing."

On budgetary matters, Bush said that with his proposed "flexible freeze" on spending, "some things will go up and then some things must be offset by going down. We're going to hold the line as we reduce the spending side of this budget . . . without raising our taxes."

But as for the pay increase, he said, "I am vice president and I will be supportive of what the president decides. I've done that for seven and eleven-twelfths years and I don't plan to change now."

"When the ball is in my court and the buck is stopping on my desk, I may have something else to say about matters of this nature," he added.

Asked for details of his flexible freeze, Bush replied, "I'll tell you when I take my message up to a joint session of the Congress."

Bush will not make a formal State of the Union address until next year, but aides say they expect the new president to address Congress a few weeks after the Jan. 20 inauguration.

In doing so, he will be following the example of Reagan, who went before Congress to appeal for his tax and budget cuts in February 1981, a few weeks after replacing Jimmy Carter.

Reagan is sending Congress a lame-duck, $1.2 trillion budget for fiscal 1990 on Monday. Administration officials say it will hold the deficit to $92 billion in part by cutting domestic programs by more than $30 billion.

"I won't have time to submit a budget this thick," said Bush, holding his hands a foot apart. "But I will have time to analyze the president's proposals - a budget, incidentally, that will go up there without raising taxes - and say, `Here's what I'll add here and take off a little there,' something of that nature.

"But it will be done. After I become president I will, as I've said all along, wrestle with that problem and then send the message up to the Hill and that will start the process."

White House spokesman Marlin Fitzwater said Friday the Reagan budget will propose eliminating 80 programs, many of them survivors of past Reagan hit lists.

"I hasten to emphasize that this is a Reagan administration budget and not a Bush administration budget," said Fitzwater, who will also be Bush's spokesman. Bush will make some alterations and change some spending priorities, Fitzwater said, "but this is not a good-cop, bad-cop exercise."