On Friday during the lunch break in the political corruption trial of Maryland Gov. Marvin Mandel and five codefendants, legislative adie Alan Wilner received a call from his ailing governor.

"He asked me to set up a meeting with the lieutenant governor the next day," Wilner recalled yesterday."I assumed what he wanted to do, but I didn't ask."

What Mandel - who had been hospitalized for 22 days for a possible stroke - had finally decided to do was to follow the advice of friends, aides and physicians and turn over the power of the governorship to Lt. Gov. Blair Lee III.

"He was moving in that direction (of relinquishing his duties)," Lee said yesterday, "but every time a wave of editorials were written demanding he step down, it set us back a week. He is a proud man."

For Lee, Mandel's decision ended several weeks of limited duty as a stand-in at state functios and behind-the-scenes administration of the state government. During those weeks Lee had to spend what he described as an "inordinate (amount of) time" making temporary decisions, then waiting for Mandel's approval before he could carry out the final policy decision.

"This transfer is probably more psychological than anything else," said Wilner. "Blair had already been handed most of the duties, but everyone will know (now) that a decision from Blair Lee will stick."

Yesterday, it was Baltimore's Macedonia Baptist Church congregation, dressed in summer linens and find straw fedoras, that heard now Acting Governor Blair Lee III rejoice on his first morning in the new office.

"I com here before you full of emotion, emotions on top of emotions," Lee told them. "This is a strange and wonderful day for me."

"What kind of time is this?" asked Rep. Barbara C. Jordan (D-Texas), one of the speakers at the church service, which celebrated the 73rd annual Women's Day. "It's the kind of time when you wake up lieutenant governor one morning and governor the next."

It was only a matter of timing, in the minds of his friends and advisors, when Mandel would annouce that he could not both govern the state and attend his political corruption trial, begun last week. Mandel admitted to reporters last week that he probably could not stant trial and govern shortly after he also discussed a possible transfer of the governor's powers with Lee for the first time.

So when Wilner called Lee on Friday to arrange for a Saturday meeting at 2 p.m. with the governor in his Annapolis mansion, Lee and other state officials were already prepared for a Mandel decision to step down as governor for the time being.

On Saturday, Mandel attended the half-day court session in Baltimore and then motored back to Annapolis for his appointment with Lee. His secret decision to transfer the power had been well-kept. Even some defense attorneys were incredulous when they later heard that Lee had been made acting governor.

Lee arrived to find Mandel with his wife, Jeanne. THe letter passing on the duties and responsibilities of the Governor of Maryland to Blair Lee III, the first lieutenant governor in the state's history and now the first acting governor as well, was already prepared.

"We talked quite a while and about appointments . . . others will come along for which he made promises, and those I will call the 'Mandel' appointments," Lee said. "Otherwise - right now all the state's legal powers are on top of my little head."

"He said he wants rest and recuperation and he does not want the little time left over after the trial day used up with state problems," Lee said of his Saturday meeting.

"The system wasn't working; he knew it and I knew it."

Lee beamed yesterday. He signed autographs after the church service with a flourish: "Blair Lee III, Acting Governor."

Finally, the Lee family has a governor, albeit acting, to add to the ancestral line of aristrocrats and politicians who signed the Declaration of Independence, commanded the Confederate Army and won election as the first U.S. senator from Maryland.

"I woke up awestruck," Lee said. "I am happy to have this challenge . . . to show my stuff. You could be lieutenant governor for 20 years and no one would know who you were."

Saturday night after the announcement, Lee kept a dinner date in Brunswick with the Petersville Democratic Club. For want of certain supplies, it was adjourned after coffee to a nearby American Legion Hall where Lee received his first toast as acting governor.

"I guarantee I'll carry Brunswick next year," Lee mumbled, cracking a slow easy smile.

Impact of what Lee hopes to achieve during his temporary spell as acting governor. Already a leader in a crowded field of gubernatorial candidates for next year's race - and apparently Mandel's private preference as a successor - Lee has, lacked the visibility to set him apart from the others.

For the seven years he has been Mandel's deputy Lee has stood in the shadows content to administer and lobby for the governor's programs and, at times, accept the blame for failures.

Before that, as the scion of the Montgomery County Lees, he was far more independent, from his brief career as newspaper publisher to his days in the General Assembly, first as delegate and then state senator.

Once Lee said, he did not have "the kind of driving ambition to reach the top, unfortunately," yet Francis Preston Blair Lee III is there now, a not unexpected product of 300 years of Lee family politicians.

A smooth, graying patrician and millionaire Lee went through the exclusive St. Paul's prep school and Princeton besides undergoing the proven Lee family raining. He wears his heritage like a mantle, yet he also carries it as a burden.

His political career has involved considerable personal and financial sacrifice, and only four years ago he wondered "how much longer I can take it."

The father of eight children and grandfather of three, Lee has undergone the trial of losing his second son, Pierre Boal Lee, who committed suicide in 1973 at the age of 27. His eldest son and namesake, Blair Lee IV, broke the line of political leadership and dreams of holding office by giving up the practice of law and moving to a Virginia farm.

Except for his sister Elizabeth Scull, Montgomery County Council member, and his nephew, David Scull, delegate to the General Assembly, only Acting Governor Lee remains the heir to his clan's political fortunes.

At first, Lee tried to escape the influence of his family and stron father, but Col. E. Brooke Lee, one-time speaker of the House of Delegates and czar of Montgomery County politics, has yet to be disappointed with his son.

When Blair Lee III took over his family's weekly newspaper after World War II, he did so only on the condition that his father not interfere. The deal was made, and the paper promptly won the Maryland Press Association's award for the best weekly three years running under Blair Lee's tutelage.

In his eight years as delegate, beginning in 1954, Lee move sharply from his father's conservative politics into a softer mold as a planner, negotiator and man willing to find the compromising center.

In 1962 Lee took the step that put him outside state politics for four years. Running on an "anti-establishment ticket," as he called it, Lee challenged Daniel Brewster for the Democratic nomination as U.S. senator and lost.

He got back into the political fold with his election to the state senate in 1966. Since then, Lee has lived within the establishment.

Throughout the scandals, beginning with former Vice President Spiro T. Agnew's resignation down to Mandel's own political corruption trial, Lee has been surrounded by but never accused of being a part of the political corruption that has earned Maryland national notoriety.