The Prince George's County Sheriff's Department is investigating the possibility that one or more sheriff's deputies illegally obtained a copy of an examination used to promote deputies to the rank of sergeant before the test was given late last month, county officials said yesterday.

Sheriff James Aluisi said he asked the county personnel office to void the examination after his office discovered that the desks of two sergeants who helped prepare the examination had been broken into during the weekend the test was given.

"We're going on the assumption that the security of the test has been compromised," Aluisi said. "It's a very serious matter."

Aluisi said he would fire any members of the force who were involved.

The Prince George's County Personnel Office administered the examination on March 29 to 41 sheriff's deputies vying for four sergeant positions, Aluisi said.

A copy of the test was kept in a locked desk drawer of one of the six sergeants in the sheriff's department who helped the county personnel office develop the test, Aluisi said. The sergeants locked their desks when they left work in Upper Marlboro on March 28, the day before the exam was given, Aluisi said. When they returned to work on March 30, the day after the exam, the desks had been broken into and papers left disheveled.

The copy of the exam was left behind in the desk drawer, Aluisi said. Nothing else in the two offices had been disturbed which, Aluisi said, indicated the intruder was looking for something kept in those desks.

Mary Godfrey, director of the county personnel office, said her office did not grade the examinations because of the allegations. Godfrey said she could not remember any other merit exam being voided for similar reasons.

Persons taking the sergeants' exam are placed on a list of department employes applying for the position, which pays between $22,607 and $30,871 a year. Aluisi said the last sergeants' exam was given in 1981 and that 61 deputies have applied for the four slots expected to be available this year. Another sergeants' exam will be given in three to four months, he said.

"This is not to make excuses for whoever did this -- and it might not have been someone in the department -- but law enforcement officers, like anybody else, are human beings," Aluisi said. "But my job now is to identify who they are and, if they are in the department, to get rid of them."