Acting Gov. Blair Lee III said today that last weekend's temporary changing of the guard in the governor's office will affect only the style of state government, not its substance.

"My style is obviously going to be different from Marvin Mandel's", Lee said at his first press conference since last Saturday when Gov. Mandel designated him acting governor for an indefinite period.

"(Mandel) was trained as city lawyer and lawyers, as everyone knows, are people who like to reveal as little as they can possibly get away with. I had my early training - God save the mark - as a newspaper reporter, and everybody knows how they behave," Lee added, provoking a chorus of guffaws, his own among them.

The very style of those remarks, laced with self-deprecating humor and a hint of camaraderie, made this press conterence different from the others that have been held in the reception room of the governor's office over the last few years.

In the place of the adroit, complex nonstatements that Mandel prided himself on, Lee's answers came back frankly and simply as he dealt with a range of subjects, from his own new post to the Baltimore subway.

Although he said he has very intention of consulting with Mandel during his indefinite stay in the governor's office. "I personally am responsible for what happens from here on.

"So I cannot. I will not be a stooge, a puppet for anybody. It's just that simple," he declared.

Nonetheles, despite his assertions of control, a lingering ambiguity remains about Lee's position. Lee underlined his caretaker role today by stressing that he would be working with the present Mandel staff members, he is charging the legal duties of governor from his old lieutenant governor's office.

Also, he said today that he would routinely make those appointments to state commissions or judgeship already had discussed with prospective appointees; Lee added that in annoucing the appointments he would note that the appointee was Mandel's choice rather than his.

Mandel designated Lee acting Governor after his doctors convinced him that the combined pressures of his ongoing corruption trial and his uncertain health already were enough strain on him. It would be unwise for him to retain the additional responsibilities of state government, they said, until the other pressures were removed.

Saturday's action formally accomplished the transfer of powers that had actually taken place gradually over the preceding weeks since Mandel was hospitalized.

"It's a reasonable guess that I will continue in this status as long as the trial lasts," Lee said today.

Admittion that his active role as a Democratic candidate in the 1978 gubernatorial race will be "sharply curtailed, he noted that "that deprivation is more than offset by the sudden visibility of Blair Lee.

"I could go on being Lieutenant governor for 20 years and stil nobody would ever hear of me. But right now I'm wallowing in the unaccustomed publicity and loving every minute of it."

Asked if he had any plans or programs, any things he wanted to get done during his indefinite term, Lee said "state government is a thing that rolls along and copes with problems that arise . . .

"When problems arise I will be the Johnny-on-the-spot to cope with them."