For this, the final important decision of his career as governor, Marvin Mandel once again was studying all the angles. He refused to be hurried as he worked out the best strategy for his all-but-certain resumption of the full powers of office he was forced to surrender 17 months ago.

"It's no longer a question of whether, but when and how," gubernatorial press secretary Thom Burden said several hours after Mandel completed an hour-long meeting with Acting Gov. Blair Lee III, a session that set the stage for a 10 a.m. news conference Monday. At that conference according to Burden, Mandel will reclaim his powers -- "there is only a minuscule chance" of any other outcome of this long-running drama.

The question of who runs Maryland has stimulated political speculation here for three days since a U.S. appeals court reversed Mandel's conviction on corruption charges and restored his title as governor. To acquire the full powers of the office for the 2 1/2 rmaining days of his second term, Mandel must only sign a letter reclaiming authority from Lee.

Over the last three days, Mandel, a deliberate and at times inscrutable man, clearly was in no hurry to make that decision. He said he needed time to celebrate his political resurrection and to fully explore how his move back into the governor's office would affect Lee and Harry R. Hughes, who will be inaugurated this Wednesday.

"Timing to him is the key to everything," said Mandel's former chief of staff, Frank DeFilippo. "Every piece has got to be in place before he makes a move. Marvin's the world's greatest chessmaster."

Today, after three days of celebrating. Mandel appeared more interested in seriously considering his alternatives, of as he said at a State House press conference Saturday afternoon, "thinking about thinking about what i'm going to do."

At the one-hour meeting with Lee at the acting governor's Silver Spring home today, Mandel took part in what press secretary Burden called "a thorough discussion" of the options. This was in marked contrast to Mandel's earlier discussions with Lee, at which Mandel "reminisced and talked about everything, except what's relevant," as Lee put it.

The simple transfer of power, when it comes, will be primarily symbolic, and just as it answers one question it will prompt another: What, if anything, will Mandel do with his restored authority before Gov.-elect Harry E. Hughes takes over at noon Wednesday.

Mandel already has said that he will not move back into the governor's mansion, which has been vacant since Lee cleared out Saturday morning. If he decides to work in his State House office, he will have to bring a desk and chair up to the second floor with him, since Lee removed most of the office furniture and shipped it back to Silver Spring.

There is very little work -- administrative or ceremonial -- to be doen by a governor in the final days of the transition. The 1980 budget already has been prepared by Lee and Hughes and has gone to the print shop. There are few vacancies on state boards and commissions that Lee neglected to fill last week.

With his resotred authority, Mandel will be able to pardon convicted felons in the state. One person in that category -- former Baltimore County Executive N. Dale Anderson -- was pushing hard to get a pardon from Lee, without success. He may renew that effort witn Mandel, who was himself, only four days ago, a man facing a four-year prison sentence.

Mandel's own legal status was being reviewed this weekend by the U.S. attorney's office in Baltimore which handled the Mandel prosecution, and by Justice Department officials in Washington.

These officials have the options of dropping the case against mandel; asking for a rehearing of last week's 2 to 4 Court of Appeals decision; or seeking a third trial.

Reached at home today, U.S. Attorney Russell T. Baker said he had "no comment" on which course his office will take.

Among the technical objections cited by the Fourth U.S. Circuit Court of appeals in overturning the Mandel verdict was one that would effectively eliminate some crucial evidence in the case.

On Tuesday, there is a ceremonial duty for a governor to perform -- the swearing-in of Rita Davidson as the first woman to serve on the Maryland Court of Appeals, the state's highest court. Davidson was appointed by Lee, and the acting governor's desire to preside at her swearing-in has been one of the factors Mandel has considered in weighing whether and when to reassume power.

The other ceremonial function for Mandel to perform is the signing of a formal certificate that commissions Hughes as the next governor.

Mandel, still awaiting word on his cinviction at the time, did not receive an invitation to Hughes' inauguration when they were sent out weeks ago. He has said, however, that he did not feel slighted by this. "By tradition," Mandel said, "outgoing governors do not take part in the inauguration. It's the new governor's day."

It is altogether fitting that Mandel would be preoccupied with the question of "when" at this juncture of his career. His sense of timing always has served him well, giving him a special advantage in acquiring influence and wielding power.

As a member of the state House of Delegates for 16 years and later as governor, he gained a reputation as the consummate tactician, the man who always seemed to know the best time to introduce legislation, how long to keep bills in committee and when to call in his chits.

Being in the right place at the right time had a lot to do with his rise as a politician. It is a testimony to good timing that be became the most powerful political figure in Maryland in 1969 without ever running for office outside of his legislative district in northwest Baltimore's Jewish community.

That year of 1969 was a turning point for Mandel. While serving as speaker of the House, he was elected by the legislature to fill the unexpired term of then-Gov. Spiro T. Agnew, a surprise vice presidential choice on the presidential ticket of Richard M. Nixon.

Mandel's meticulous concept of timing often leaves his advisers and allies in the dark about his thinking. It is a common story that two opposing factions can argue their case before him, each leaving with the understanding that he was siding with their position.

"Everything is like a munitions factory to Marvin,' said his long-time aide, DeFilippo. "Everybody makes a piece of the gun. He's the only one who knows how each piece fits together." CAPTION:

Picture, After Blair Lee III had his desk removed, the governor's office in Annapolis was left with a rug and several chairs, plus the Maryland and United States flags, By Joel Richardson -- The Washington Post