WASHINGTON (AP) _ Authorities should ban the use of alcohol by commercial bus or truck drivers and impose tighter standards on when such drivers would lose their licenses for drinking and driving, a National Academy of Sciences panel said today.

In a report ordered by Congress, the NAS said a stiffening of the laws against commercial drivers' drinking and vigorous enforcement by police would save as many as 250 lives and prevent thousands of highway injuries a year.

''Any consumption of alcohol on the job by commercial vehicle drivers is inappropriate ... and incompatible with traffic safety,'' the special committee of the academy's Research Council said in the report to the Department of Transportation.

The department must decide within a year on a national alcohol standard for truck and bus drivers and it is expected to rely heavily on the conclusions of the year-long study and report released today.

States would have to comply with the national standard or risk the loss of part of their federal highway money.

States currently consider a commercial truck or bus driver impaired and subject to criminal penalties when a blood alcohol level of 0.10 percent is found, the same level used in cases involving non-commercial drivers.

But the Research Council panel, which included a cross-section of experts, said the level at which a driver is considered under the influence should be lowered from 0.10 percent to 0.04 percent because of the increased hazards posed by large trucks and buses.

Drivers of such vehicles should be subject to a loss of license - one year for first offenses and permanently for second offenses - with a blood alcohol level of 0.04, the study concludes. Furthermore, it said, the driver should face a 30-day suspension if any alcohol whatsoever is found in blood tests.

The report said there are about 750 fatal highway accidents a year in which a driver of a truck or bus is found to have been drinking.

Truck accidents overall kill nearly 6,000 people a year, about 80 percent of them in other vehicles or pedestrians, and the research group said the special hazards posed by large trucks and buses warrant tighter alcohol curbs.

The weight and size of such vehicles, limitations on highway design and fatigue among truck and bus drivers make the effects of alcohol at lower blood levels more hazardous than among drivers in the general public, the report said.

''In short, the majority of the committee believes that the (blood alcohol) standard for commercial vehicle drivers should be zero and that the penalties should be graduated to match the offense,'' the report said.

Nevertheless, several of the panel members favored leaving the blood alcohol level for truck and bus drivers at 0.10, suggesting that the steps needed to enforce the lower levels, notably more sophisticated breath- screening devices, may be unconstitutional.

The year-long study was directed by Congress in a 1986 law that requires the secretary of transportation to establish by October 1988 a national standard at which a commercial bus or truck driver would be considered to be legally under the influence of alcohol and subject to license revocation.

If no action is taken, the 0.04 standard automatically will go into effect.

The law also requires each state to enact legislation reflecting the federal standard. States failing to comply with the standard could have up to 10 percent of their federal highway money withheld.