WASHINGTON (AP) _ President Reagan took the first steps Thursday toward an amiable transition of power to President-elect George Bush, leaving instructions for Cabinet officers and other political appointees to turn in their resignations by inauguration day on Jan. 20.

The new president and the old met with White House chief of staff Kenneth Duberstein and later attended a Cabinet meeting as Bush began the work of assembling his administration.

The president-elect also met with Craig Fuller and Bob Teeter, leaders of his transition office, before flying off to a long weekend of fishing in Florida, his first post-election vacation.

Vice President-elect Dan Quayle also met with leaders of Bush's transition team.

The Bush transition office officially opens for business on Monday, but the telltale signs already were in place in a rented suite of offices a few blocks from the White House. Security guards erected metal detectors and a desk was set up at the entrance where a volunteer collected resumes from job-seekers.

The vice president made his first Cabinet appointment on Wednesday, naming campaign chairman James A. Baker III to be his secretary of state. He has told reporters he wants to name the balance of his Cabinet sooner rather than later, but has set no timetable.

Reagan and Bush were applauded as they walked together into a Cabinet meeting. Fitzwater quoted Reagan as saying, ''We don't even argue over which side of the table to sit on.''

But for all the friendliness, White House spokesman Marlin Fitzwater said Reagan reminded his men, ''We are still in charge until Jan. 20 and are still responsible for making decisions of the government.''

Duberstein told the Cabinet and heads of independent agencies to be prepared to submit their resignations. ''It is probably fair to say that all political appointees at all levels should be prepared to resign or depart on Jan. 20,'' said Fitzwater.

''President Reagan of course is free to accept anyone's resignation at any time and the president-elect would have that decision to make after the 20th,'' he said. ''There might be cases where he wouldn't have someone to fill that position, and would want someone to stay on for awhile,'' he said.

Bush on Wednesday promised a ''brand new team'' when he takes office. But Treasury Secretary Nicholas Brady, Attorney General Dick Thornburgh and Education Secretary Lauro Cavazos all have been mentioned as possible holdover appointments.

One man viewed as likely to receive a major post in the new administration, outgoing Gov. John Sununu of New Hampshire, set his goals high. He told reporters in New Hampshire that he would turn down offers to be secretary of education or energy, but White House chief of staff ''isn't on my 'no list.''' Sununu, who campaigned energetically for Bush and was instrumental in his critical victory in the New Hampshire primary last February, said he hadn't been offered any post.

On day two after the election, the rumor mill was working at full speed.

The names spit out included former Sen. John Tower of Texas; former Rep. Jack Edwards of Alabama or former National Security Adviser Brent Scowcroft for the Pentagon; defeated Maryland Senate candidate Alan Keyes, a former diplomat, as a possible ambassador to the U.N. and defeated Ohio Senate candidate George Voinovich, the mayor of Cleveland, for housing and urban development.

Ohio Rep. Bill Gradison's name circulated through the Department of Health and Human Services as a possible replacement for Otis Bowen.

A long list of names made the rounds at the Agriculture Department, including Clayton Yeutter, currently the U.S. Trade Representative.