The Senate is preparing to take up a $28 billion transportation spending measure for next year that would severely penalize states that do not enact laws suspending driver's licenses of drug offenders for at least six months.

The Senate measure, which would take effect in 1993, would withhold 5 percent of federal highway funds during the first year a state does not have a law revoking drug offenders' driving privileges. In later years the penalty would be 10 percent. The Senate measure, however, would exempt a state whose governor or legislature certifies or resolves that it is opposed to enacting a law that links the driving privilege to a clean drug record.

During a House debate, concerns were raised about the constitutionality of linking suspension of a driver's license to anything but a person's driving record. But the House eventually voted to withhold 2 percent of the highway funds from a state that does not revoke drug offenders' licenses without a provision exempting a state that declares it does not want to enact such a link.

The Senate transportation appropriations bill, approved last week by its Appropriations Committee, also proposes to ban the use of radar detectors by truck drivers and other commercial vehicle operators. Many states already prohibit detectors.

The ban is supported by the American Trucking Association and a number of safety groups, including the Insurance Institute for Highway Safety, Public Citizen and the National Safety Council.

"There's only one use for a radar detector and that's to violate the speed limits," said an official of the American Trucking Association, which represents trucking companies that hire truck drivers. The language was inserted into the transportation bill last week by Sen. Frank R. Lautenberg (D-N.J), chairman of the Appropriations subcommittee on transportation and related agencies.

The ban would take effect within 270 days of the bill's becoming law.

The transportation measure or the accompanying Appropriations Committee report also:

Directs that local airport authorities that use federal funds to abate noise from jet aircraft award soundproofing grants to parochial and private schools located in noise corridors, not just to public schools. Language was included in the legislative report at the request of the Port Authority of New York and New Jersey, which reportedly is concerned about a legal challenge from the Federal Aviation Administration if it continues to do soundproofing work at non-public schools.

Retains a House-passed directive that prohibits the withholding of federal highway funds from Maryland and four other states in which federal investigators have determined too many drivers are exceeding the national speed limit of 55 mph. The Senate report cited the "absurd inequity" of the law. It notes that a state with 55 mph laws can be punished when drivers exceed that limit while a state that raises its speed limit to 65 mph is exempt from loss of highway funds under the national speed limit law.

Chastises the Coast Guard for the escalating costs of its fleet renovation and modernization program, but nevertheless provides $12.7 million more for the program than requested by the president. "Originally budgeted as $594 million, current estimates put final costs as high as $871 million," the committee noted.