Marvin Mandel will keep one of the perquisites of the office of governor - state police bodyguards - after he is sentenced next month on political corruption charges.

Acting Gov. Blair Lee today told Capt. Norval F. Cooper, chief of the 19-member Executive Security Division of the Maryland State Police, that plainclothes protection of Mandel should continue "for an indefinite period of time" after his sentencing in federal court on Oct. 7.

The decision by Lee was prompted by a suggestion from Col. Thomas S. Smith, superintendent of State police, according to Tom L. Burden, Lee's press aide. In a letter to Lee dated Sept. 19, Smith said it would be "reasonable" to continue guarding the ex-governor because of written and telephoned threats directed to Mandel following his conviction Aug. 23.

Lee talked to Smith this morning and then told Cooper this afternoon to prepare to provide "adequate protection" for Mandel after his appearance in the Baltimore courtroom next month. Lee's order presupposes that Mandel will be out of prison, either because the sentence might not call for his incarceration or because he could remain free pending his appeal of the conviction.

Burden declined to discuss details of the protection, citing "security reasons." But he emphasized that the order affects only Mandel. State police officers now also protect Mandel's wife, Jeanne, and her children, serving as chauffeurs who take the children back and forth to private school.

Although no one would reveal how many officers would be assigned to Mandel, Lee said the order would not require additional personnel, presumably because there will be no lieutenant governor for the officers to protect. Lee indicated officers assigned to mandel would have use of an unmarked state police car, but it was not clear if the troopers would continue to double as chauffeurs to Mandel.

Burden said Mandel told him that he did not seek the protection and had not discussed the idea with Lee.