Attorneys for Navy Cmdr. Donal M. Billig began his defense yesterday, presenting testimony from a recruiter that the former Bethesda Naval Hospital heart surgeon had disclosed previous professional troubles when he applied to join the Navy in 1982.

But Lt. Cmdr. Jerry D. Penn also said he learned later that Billig had lied about the extent of those past problems, a piece of evidence that may have bolstered the prosecution's case.

The defense began as the court-martial entered its sixth week and followed testimony by more than 40 witnesses for the prosecution, which has attempted to portray Billig as an incompetent physician, handicapped by deficient eyesight and burdened with a history of professional failures.

Billig, 54, is charged with involuntary manslaughter in the deaths of five patients and 24 counts of dereliction of duty in connection with heart surgery he conducted at Bethesda from June through September 1983.

Defense attorneys -- who are expected to call about nine witnesses and put Billig on the stand later this week -- have argued that their client was honest with his Navy recruiters and employers and that he was declared physically fit for duty. In opening arguments Jan. 9, attorney Denver Graham said Billig used his best medical judgment in treating patients and employed proper procedures in the operating room.

Penn, who is charged with perjury for his role in recruiting the surgeon, testified yesterday that Billig provided information about his poor eyesight. He said Billig also told him that an incident at a New Jersey hospital had led him to voluntarily surrender his privileges there and his license to practice medicine in that state.

But Penn admitted under cross-examination that he later learned, after Billig had been commissioned, that Monmouth Medical Center officials had found that Billig "lacked technical, surgical competence" and stripped him of his privileges.

"Does that square with what the accused told you?" prosecutor Lt. Cmdr. Joseph G. VanWinkle asked the recruiter.

"No sir, it does not," answered Penn, who was testifying under a grant of immunity.

The defense also offered testimony yesterday from Dr. Mansour Armaly, professor of ophthalmology at George Washington University. Armaly, who examined Billig in October and December last year, said that it is impossible to judge now the quality of Billig's eyesight in 1983 and 1984, when he was practicing at Bethesda. That contradicted prosecution witnesses who testified that Billig's eyesight should have kept him from performing surgery.

But Armaly also testified that Billig, whose eyesight was damaged when he was hit in the face by a tennis ball in 1978, had suffered a "near total loss" of "stereopsis," the ability to see objects in three-dimensional form.