The Bexar County medical examiner ruled today that Sante Alesandro Bario, a celebrated Drug Enforcement Administration agent, died as the long-delayed result of choking on a peanut butter sandwich.

Bario, noted for his undercover investigations throughout the world, had been in county jail under federal indictment on a charge of accepting a bribe in a cocaine smuggling case.

On Dec. 16 he choked and went into convulsions while eating the sandwich in his cell. He never regained consciousness and died last Tuesday in Santa Rosa Medical Center here.

An early hospital lab report had suggested the possibility that Bario had suffered strychnine poisoning, and attorneys for his family arranged for the presence of Dr. David Spain, professor of clinical pathology at New York University, at the autopsy.

No poisons were detected, Dr. Rubin Santos, county medical examiner, said today in issuing a ruling of probably accidental death.

He said the autopsy finding was of death from bronchial pneumonia which, in turn, was a complication of partial brain death, which was secondary to airway obstruction by the sandwich.

Santos said that initial tests had shown Bario was under the influence of a "near toxic level of Elavil," an anti-depressant, when he choked and that this was a contributing factor.

He explained that the anti-depressant produces severe dryness of the mouth and difficulty in swallowing.

"If it had not been for that, he probably would have been able to take care of that sandwich," Santos commented.

The medical examiner said no poisons were detected either at Bario's admission to the hospital or during the autopsy.

He said the report of strychnine poisoning was the result of a misinterpretation during a screening procedure at the time of the initial hospital tests.

Santos said microscopic studies will confirm "what we have seen during the autopsy."

He said pathologist Spain left the regional crime labor with the "impression no posion was involved," and took with him two minute pieces of tissue for additional tests.