Cmdr. Donal M. Billig, a heart surgeon charged with involuntary manslaughter in the deaths of five patients at Bethesda Naval Hospital, performed "technically adequate" operations on his patients and should be cleared of charges, said defense attorneys who yesterday portrayed the doctor as the victim of an "administrative mess" that led to a recommendation for court-martial.

In closing arguments to a Navy pretrial investigation, Lt. Cmdr. Stephen P. Baker argued that a previous internal investigation by the Navy, which resulted in the court case, was "biased and way off the mark" in determining that the surgeon was negligent in his actions.

Navy Commodore H. James Sears, the investigating officer, said yesterday he expects to rule no sooner than Oct. 18 on whether to recommend to Navy officials that a court-martial be held.

Billig, 54, faces five counts of involuntary manslaughter and 24 counts of dereliction of duty for operating without proper supervision while at the hospital from January 1983 through November 1984. He was recommended for court-martial based on an internal review by a Navy board in July. The pretrial investigation was launched at Billig's request.

Baker's statement yesterday followed testimony from Army Col. Russ Zajtchuk, a cardiothoracic surgeon who testified earlier in the week about his supervision of Billig from January through July 1983.

Attorney Denver Graham, a civilian lawyer assisting in the Billig defense, made repeated attempts to discredit Zajtchuk, who earlier described Billig as incompetent and harshly criticized the surgical judgments made by Billig during a heart operation on retired Air Force Lt. Col. John L. Kas Jr.

Yesterday, Zajtchuk called Billig "cocky" and said a cardiac pump procedure that the surgeon attempted during the operation on Kas, who died last October, was "not a good method . . . because it would not do the job.

"You can do a lot of things by cutting corners and doing things stupidly . . . Dr. Billig needed all the help he could get. For him, to cut corners is a mistake," Zajtchuk said.

Baker discounted Zajtchuk's remarks later as the opinion of "one very arrogant and argumentative surgeon who obviously doesn't like Dr. Billig." Baker argued that the government had not shown that the deaths resulted from negligent practices by Billig or that the 24 other cases in which the doctor was charged were unauthorized or unsupervised operations.

Pointing out that Bethesda officials had testified that Billig was given written permission to operate on all heart cases but told privately that he was restricted to routine cases, Baker said the dereliction of duty charges were "an outgrowth of the medical corps administrative mess at Bethesda Hospital . . . It is evident that Dr. Billig could have made an honest mistake about what he could and could not do," Baker said.