ORLANDO, Fla. (AP) _ Two former employees of the company that makes the Pershing 2 missile have been charged with defrauding the government of $144,000 by billing for equipment that never was received, the FBI said.

The former president of a retail computer outlet in Gainesville also was charged.

Martin Marietta Aerospace, prime contractor for the Pershing 2 missiles being deployed in Western Europe, tipped the FBI, said Special Agent Perry Doran.

''Yes, we blew the whistle on them,'' said a Martin official who would not give his name. ''We found it in our own audit, worked with our own security, then turned the case over to the FBI.''

Charles Deneen III, 31, of Orlando was charged in an indictment Wednesday with 22 counts of mail fraud, filing of false statements and conspiracy. He was manager of the Orlando plant's business operations and responsible for buying support equipment on the missile project.

Deneen's assistant, William Welch, 34, of Eustis, and Timothy Strickland, 23, of Alpharetta, Ga., each were charged by authorities with one count of conspiracy.

Deneen will plead innocent to the charges, lawyer Harrison Slaughter said Thursday, adding that no arraignment date had been set.

Welch's lawyer, Tom Mihok, declined comment on the case. There was no telephone listing for Strickland in Alpharetta, Ga.

Deneen and Welch resigned from the company in September 1984. Strickland was president of Compumax Corp., a retail computer outlet in Gainesville.

The federal complaints said that from November 1983 to September 1984, Deneen and Welch obtained Commodore 64 computers and related equipment from Strickland and resold them to the public at a computer business they owned in Eustis.

They falsified Martin invoices, claiming the computers and electronic components had been shipped by Strickland and received by the company, according to the charges.

The invoices were submitted to the U.S. Army for reimbursement, officials said.

If convicted, Deneen could be sentenced to 115 years in prison and fined $103,000. Welch and Strickland each face up to 10 years in prison and $10,000 in fines.