Cmdr. Donal M. Billig, the former head of cardiothoracic surgery at Bethesda Naval Hospital, has been formally ordered to face trial on five counts of involuntary manslaughter and 24 counts of dereliction of duty.

Billig had been referred for court-martial in June after an internal investigation by the Navy recommended that he face four counts of involuntary manslaughter plus the counts of dereliction of duty.

The new court-martial order came this week as a result of a separate pretrial investigation in September, which Billig requested in an effort to challenge the previous investigation.

The fifth involuntary manslaughter charge, stemming from the death of a retired Air Force lieutenant colonel in October 1984, was disclosed in court proceedings last month.

Neither Billig or his attorneys could be reached for comment yesterday. They have repeatedly declined to comment on the charges.

Rear Adm. Joseph Cassells, chief of the Naval Medical Command, reviewed the results of the new investigation, held at the Navy Yard last month, and recommended Thursday that Billig face court-martial.

Billig, 54, began working at Bethesda Naval Hospital in January 1983 and became head of the cardiothoracic unit in June 1983. His hospital privileges were suspended in November 1984 when questions about his surgical competence were raised by officials there.

Another hearing is scheduled for Monday to consider a defense motion challenging the investigating officer's impartiality during the recent pretrial hearings. Commodore James Sears, who reviewed the case and recommended the new court-martial orders to the Naval Medical Command, also participated in the internal review and wrote the report that accompanied a recommendation for court-martial.

The defense argued before the pretrial investigation that Sears' previous involvement with the case should have made him ineligible to participate in the new investigation. The defense has asked to argue that point again, the Navy said yesterday, and the prosecution plans to request a trial date.