The Supreme Court has been asked to decide whether the Constitution allows a motorist's refusal of a test for possible drunkenness to be admitted into evidence at his trial.

A Department of Transportation estimate bears on the importance of the issue: year after year, at least half of the nation's auto fatalities involve alcohol in some amount. The number of fatalities in 1978 was 50,145.

The issue was left open by the court in 1966, when it held that the Fifth Amendment's protection against compelled self-incrimination did not prevent the use at trial of an analysis of a blood sample taken from an apparently intoxicated driver without his consent.

As of last spring, the District of Columbia and about nine states, including Maryland and Virginia, prohibited trial judges from admitting a motorist's refusal to take a breath-analysis or blood test for possible intoxication, according to Bertrand J. Kahn of the Legal Aid Society in New York City. The prohibition is based on laws in some jurisdictions and on court rulings in others.

By contrast, Kahn said, about 15 states, including California and New York, permitted prosecutors to use refusals in trial courtrooms.

The case before the court arose from a 1975 accident in Bronx County, N.Y., where a cab left a highway and came to rest against a chain-link fence. The driver who had leased the taxi, Herman Thomas, was slouched over and bleeding profusely from a head wound.

Police officers, leaning into the passenger compartment, found the odor of alcohol "heavy" and saw a wine bottle, more than half empty, on the floor by the front seat.

Thomas, hysterical and saying he was hurt, asked to be taken to a hospital.

There, an officer warned him that he was under arrest for driving while intoxicated, that a refusal to take a chemical test could result in revocation of his license even if ultimately he were acquitted, and, finally, that a refusal could be admitted into evidence against him.

But Thomas, saying he understood the warnings, refused to submit to a blood test. He denied he had been drinking and said he'd been unaware of the wine bottle.

Thomas was convicted of a reduced charge of driving while "impaired." The conviction was upheld on appeal.

In a petition for Supreme Court review, the Legal Aid Society argued that the privilege against compelled self-incrimination is violated by a New York State law allowing admission of a refusal to submit either to a breath-analysis or a chemical test for intoxication.

But the state countered that because the 1966 decision lets a suspect be compelled to submit to a test, he has no constitutional right not to take one, and, consequently, can't invoke the protection against compelled self-incrimination.