Three SmithKline Beckman Corp. physician-executives who failed to tell the Food and Drug Administration of grave reactions to a medicine called Selacryn yesterday let pass a deadline for changing their pleas of no contest to 14 criminal charges.

In doing so, the corporate executives left themselves open to a possible jail sentence. But an order signed by the judge in the case indicates that such a sentence is unlikely.

Drs. Philip J. Tannenbaum, Ralph M. Myerson and Theodore Selby had pleaded innocent to charges that they failed to disclose adverse reactions to the drug as required by FDA regulations. But at a Dec. 12 hearing before Federal Judge Edward N. Cahn in Allentown, Pa., they switched those pleas to no contest, with the government agreeing to make no sentencing recommendation. Cahn had set yesterday as the deadline for them to exercise an option to restore the not-guilty pleas.

The hearing record left him "not inclined" to jail the defendants, Cahn said in an order made part of the public record Dec. 26. "However, the court will require a pre-sentence report," he wrote. If it "reveals facts not previously disclosed in regard to the culpability of the individual defendants, the court reserves the right to impose the sentence of incarceration."

The order set sentencing for Feb. 25 in Philadelphia.

The maximum possible punishment on each of the 14 counts is up to a year and a $1,000 fine. SmithKline has pleaded guilty to all 34 counts in a criminal information filed in June and faces a maximum penalty of a $34,000 fine.

The Smith Kline & French Laboratories division sold Selacryn -- widely prescribed for high blood pressure -- from May 2, 1979, to Jan. 15, 1980. That day, at a meeting called by the FDA, SK&F revealed for the first time that it knew of 52 cases of liver damage, including 30 cases of jaundice and five deaths. The FDA asked for, and got, an immediate sales halt. Researchers have estimated the final U.S. toll at 25 fatal and 315 nonfatal cases.

The government, in a basically undisputed summary presented at the Dec. 12 hearing, charged that the three defendants had failed to assert their "authority and opportunity" to report "unexpected" and other serious injuries as required by FDA regulations. Their counsel said that information that should have been reported "dropped through the cracks" at SmithKline.