Maryland's Acting Gov. Blair Lee III said yesterday that his job would be easier if convicted Gov. Marvin Mandel resigned his office, allowing Lee to become Maryland's chief executive in name as well as in fact.

Lee's statement came just a few hours after Maryland Attorney General Francis B. Burch issued an opinion saying that Lee would remain only "acting" governer until Mandel exhausts all possible appeals of his mail fraud and racketeering conviction or resigns.

Burch said that under state law, Mandel will forfeit his office, his $25,000 annual salary and the perquisites of being governor - including the mansion and the state's pleasure boats - but not his title, after he is sentenced Oct. 7. His rights to a pension and police protection are still unresolved.

Burch said in his opinion that "a Lieutenant Governor who temporarily fills the office from which the Governor has been temporarily suspended because of a criminal conviction does not in the pure and ultimate sense of the term hold the office of governor."

Lee said yesterday afternoon that he has "mixed emotions" about the possible resignation of Mandel, who was convicted Tuesday of 17 counts of mail fraud and one count of racketeering. "I am even reluctant to nudge him in any direction," Lee said.

But when asked if Mandel's resignation would make his job easier, Lee replied: "Yes, it would. It would clarify things . . . removing doubts, questions, the tentative nature of what will be my function beginning Oct. 7."

One state job left in limbo as a result of Burch's opinion is the lieutentant governorship.

As long as Lee remains Acting Governor, Burch said, he may not appoint a lieutenant governor, since "there is no vacancy in the office of lieutenant governor unless and until you [Lee] should finally succeed to the office of Governor."

When Lee does become governor, Burch added, he would have the right to appoint a lieutenant governor, subject to the consent of a majority of the state legislature. Until then Lee must serve as both the acting chief executive of Maryland and as the chief executive's deputy.

At his press conference in Annapolis yesterday, Lee indicated that he remains ambivalent about the possibility of naming a lieutenant governor. He said he would like someone to help shoulder his reponsibilities, but the task of naiming someone to the state's second-highest post would force him to "make prematurely" the "political decision" of who would be his running mate in the 1978 gubernatorial campaign.

Neither Burch nor Lee, both candidates for the Democratic Party's gubernatorial nomination in 1978, commented directly yesterday on the political implications of their statements.

Both men seemed to be making a conscoius effort to avoid the appearance of making political capital out of Mandel's downfall.

Another decision facing Lee is the question of whether he will move into the 50-room governor's mansion in Annapolis when Mandel is sentenced in October.

According to Burch's ruling, Lee has the option of deciding whether he would like to move his family into the mansion. But Mandel, Burch said, has no choice: After his sentencing, he must move out.

Lee refused yesterday to directly answer any questions about where he intended to live. The most he would sya, after being prodded by reporters, was "I'm going to consult my wife."

When Lee was asked about the possibility that Mandel might stay on at the mansion after Oct. 7, as Lee's guest, the acting governor replied that Mandel has already started to consult with real-estate agents in an effort to find a new home.

At the moment Mandel and his wife Jeanne have no home other than the governor's mansion.

Besides forfeiting the powers of his office - which Mandel had already turned over to Lee shortly after the start of his second trial in June - the governor must also forfeit his rights to the use of the state yacht "Maryland Lady," the servants at the governor's mansion and the use of state cars and state troopers as chauffeurs.

All these perquisites are Lee's if he wants them, after Mandel's sentencing, Burch's ruling said.

Howerver, Burch added, Lee does not have to accept the governor's salary after Mandel's sentencing. Instead, he may continue to receive the $44,856 annual salary allotted to him as lieutenant governor - a salary $20,000 greater than the governor's.

Since Lee will be assuming the responsibilities of the state's two highest offices, Burch said, he will be entitled to keep both his own staff and the team of aides assembled by Mandel.

The fate of Mandel's inner circle - which includes some of the convicted governor's closest associates and political operatives - has been a topic of wide speculation in recent days.

One staff aide, Frank H. Harris, who is a close friend of Mandel, offered his resignation yesterday, according to Lee, but no decision has been made whether to accept it.

"We [Lee and Harris] parted friends," Lee said. "I told him life can be hard, and he agreed."

Burch also took time at his press conference in Baltimore to praise Mandel as an "outstanding governor of this state.

"In my opinion," Burch said, "he's been one of the best governors in the United States. He's had his problems. He's done things I probably wouldn't have done, but I wouldn't want to fault the man for what he did as governor of this state.

While Burch and Lee were making their statements yesterday, Mandel was on his way with his wife to an unidentified location, where they intend to spend "a few days," according to Mandel press aide Thom Burden.