Legislation to ban undetectable plastic firearms could clear the Senate Judiciary Committee this Thursday, just two days after the House approved a similar bill with a calm that rarely accompanies gun control measures.

A smooth ride for the legislation was virtually assured two weeks ago, after Attorney General Edwin Meese III and law enforcement groups agreed to a compromise version - and the National Rifle Association went along.The NRA agreed to avoid a bruising gun control battle in Congress when it became clear that no existing handguns would be prohibited under the agreement.

Plastic guns are not yet a reality, but chief House sponsor William J. Hughes said Tuesday the firearms could be a weapon of choice for terrorists in the future. His colleagues agreed, passing the bill 413-4.

The Senate Judiciary subcommittee on the Constitution, meanwhile cleared a similar bill by Sen. Howard M. Metzenbaum for action by the full committee. The full panel meets again on Thursday, and the gun bill is on the agenda.

The Hughes bill would make it illegal to manufacture, import, sell, transfer or possess a plastic firearm, defined as a weapon with less than 3.7 ounces of metal.

Maximum penalties would be five years in prison, and fines of $250,000 for individuals and $1 million for organizations.

The bill contains a "sunset" provision that would repeal the criminal provisions after five years, enabling the law to keep pace with any advances that may occur in firearms detection technology.

Voting against the House measure were Republican Reps. Dick Cheney of Wyoming; Philip Crane of Illinois; Norman Shumway of California and Barbara Vucanovich of Nevada.

Hughes' bill was introduced before the administration-police compromise, but embodies the same concept.

The more precise language is in the Senate version, which would establish a detectability standard that would permit detection of the same weapons as the Hughes bill. However, it does not provide for a minimum content of metal in the gun.

Both measures would detect all existing hand-guns, thus keeping them legal for law-abiding owners. But plastic weapons that failed to meet the same metallic standard would be prohibited.

Metzenbaum, D-Ohio, called the House vote "a major step in the right direction. I look forward to working with Congressman Hughes to make sure the Congress sends the president the strongest bill possible," he said Tuesday.

Hughes said he saw no problem in working out a compromise between the House and Senate language.