Maryland's acting Gov. Blair Lee III told a meeting of AFLCIO leaders here today that he intends to avoid any state tax increases in Maryland "for the remainder of the decade."

In his first major speech since the conviction of Maryland Gov. Marvin Mandel on mail fraud and racketeering charges last week, Lee studiously avoided any direct mention of Mandel. Instead, Lee, who is a candidate for the Democratic gubernatorial nomination in 1978, stuck to a host of politically safe topics.

"If I can keep the lid on spending programs during the next General Assembly session - which I intend to do - we will be in good shape in this state financially," Lee told the crowd of 400 labor union members who had gathered in the ballroom of the Lord Baltimore Hotel.

Reminding his audience of "his unpopular prediction" in 1976 that there would be a state tax increase in 1977, Lee added "today, I can predict that you will probably see no further state tax increases for the remainder of this decade . . . perhaps longer.

"And I don't make this prediction lightly," he said, "I intend to live by it."

While avoiding the sensitive subject of Marvin Mandel during his prepared remarks to the audience, Lee did discuss some of the questions raised by Mandel's conviction during an impromptu press conference in the hotel's lobby following his luncheon remarks. Lee noted that he and his wife Mimi would be moving into the 50-room governor's mansion in Annapolis "sometime in October."

According to an opinion issued last week by Maryland Attorney General Francis B. Burch - himself a gubernatorial candidate - Mandel and his wife, Jeanne, must vacate the mansion after Mandel's sentencing, which is scheduled for Oct. 7.

Lee, who said last week before Burch issued his opinion that he would not press Mandel to leave the mansion, said today, "My wife and children and I kicked it around for most of the weekend . . . and it would be reasonable to assume that Mrs. Lee and I will be moving in (the governor's mansion) in October.

The last conversation Lee said he had had with the convicted governor was last Wednesday morning two days before Burch issued his opinion.

Although Lee's remarks during the luncheon obviously were intended to make political capital with the state's powerful labor leaders, he said afterward that he did not intend to begin campaigning in earnest for the gubernatorial nomination until next July.

"I think a campaign for a September primary ought to start in July of that year," he added. Then Lee smiled slightly and chuckled. He might do "a little judicious organizing" before that time, he conceded.

Lee's tax proposals were regarded as "realistic" by State Del. Benjamin Cardin (D-Baltimore) who is chairman ofs the House Ways and Means Committee. "I believe as well that we can do without (a tax increase) for the next couple of years.

"It's going to be tough," Cardin added. "It's going to take a major commitment of the executive and legislative branch."

The Maryland State sales tax was raised by 1 cent during the last legislative session this spring. But Cardin said the state income tax has not been chaged from the present graduated formula since 1967.