Elvis Presley was not killed by any recent drug abuse but he could have been killed by a combination of three dangerous medical conditions, the doctor who performed the autopsy on the famed singer said yesterday.

Two of the three were unsuspected by Presley's doctors, Dr. Jerry T. Francisco, the state of Tennessee's chief medical examiner, said in an interview with The Washington Post.

These were a heart enlarged by about a third and some atherosclerosis, or clogging, of the coronary arteries that feed the heart. The enlarged heart, Francisco said, was caused by the only worrisome illness that was plain before Presley's death - moderately severe high blood pressure of at least four years' standing.

Francisco, 45, is also a professor of pathology at the University of Tennessee medical school in Memphis. Doctors in other parts of the country, including District of Columbia chief medical examiner Dr. James Duke, call him an expert judge of causes of death.

Some press reports yesterday included allegations that Presley took or injected abusive drugs, like "uppers," "downers," morphine and cocaine.

Fracisco said he found no new or old needle marks on Presley's body, no accumulation of drugs in his stomach and no corrosion of the stomach lining of the sort that would indicate recent heavy drug-taking.

"I can find no evidence of drug abuse," he summed up. "We haven't completed all the toxicological tests, but I feel as confident as I can be that drugs played no part in his death."

But Francisco painted an overall word-picture of an old body for a man of 42, a body beset by many ailments.

And he said there could also be some still unknown contributor to Presley's death, since neither the coronary disease nor anything else by itself had "the degree of severity" that could by itself have stopped Presley's heart.

Francisco did the autopsy on Presley Tuesday night, then officially stated the cause of death as "cardiac arrhythmia" with "ventricular fibrillation" - in short, a heart that beats abnormally, then stops - "due to unknown causes."

He conceded yesterday that even ascribing the death to this form of heart attack was a "presumptive" diagnosis - a presumption in ordinary language - made in the absence of any positive finding of clear-cut, unmistakable cause.

Thousands of death certificates are filled out in his way every year, since the clues to heart disease are often tentative and there is frequently no sign that says, "This is it:"

Francisco said he believes a "combination" of factors produced the heart disorder, and further tests now under way may or may not turn up a clinching cause. One of the world's leading cariac pathologists Dr. Jesse Edwards of Miller Hospital of St. Paul, Minn., long of the Mayo Clinic, said it would be somewhat unusual but far from rare for a combination of high blood pressure, heart enlargement and coronary artery disease to cause a heart to stop.

Dr. George Nichopoulos, Presley's doctor and friend, told reporters in Memphis Tuesday night Presley had been taking appetite-suppressing drugs but they did not contribute to his death. He said he had also been presribing drugs for hypertension (high blood pressure) and colon, or intestinal problems.

Amphetamines - nicknamed "uppers" - are often prescribed as appetite-suppressers, and barbiturates - "downers" - are sometimes used to help calm the colon. Nichopoulos could not be reached yesterday to say just what drugs he prescribed.

Presley, who weighed more than 200 pounds, had been sick many times in the past four years. His high blood pressure was first diagnosed in 1973 after he was hospitalized for 16 days for "recurrent penumonia."

In January, 1975, he was hospitalized for 17 days for what his doctors called intestinal blockage. He was hospitalized seven months later for high blood pressure and the intestinal problem.

Last April he canceled several performances and was hospitalized for four days for intestinal flu and fatigue.

Upon Presley's release. Nichnopoulos said the singer had never been in better health. "He has a good outlook and he feels good," Nichopoulos said.

As it turned out, however, Presley was dead at the same early age of 42 at which his mother died when he was an Army private. Her death was ascribed to a heart attack, too.