State laws allowing "moments of silence" for meditation or prayer in public schools do not coerce students but simply "enhance the opportunity to pray," lawyers for Alabama and the Reagan administration told the Supreme Court yesterday.

But Mobile attorney Ronnie Williams, representing a man who challenged Alabama's law, said the state was trying to "promote religion on impressionable students," something that he said was forbidden by the Constitution.

The moments of silence law was a "blatant attempt to do through the back door what you can't do through the front door," Williams argued, referring to the Supreme Court's ruling in 1962 that prohibited teacher-directed or official prayer sessions in public schools.

The justices have never ruled on moments of silence, an approach thought to have a better chance of court approval because it avoids explicit official endorsement of prayer.

About 22 states, including Maryland and Virginia, have similar laws.

The case argued yesterday, Wallace v. Jaffree, attracted national attention last year when U.S. District Court Judge Brevard Hand ruled that the Supreme Court was wrong to ban official prayer and upheld two Alabama laws, one permitting moments of silence, the other permitting teacher-led prayer.

A federal appeals court overruled Hand. The Supreme Court last April summarily affirmed the appeals court's ruling on teacher-led prayer, but agreed to hear argument on the moments of silence statute.

The high court in recent terms has been relaxing its traditional restraints on separation of church and state, and several justices yesterday, including Chief Justice Warren E. Burger and Justice Lewis F. Powell Jr., indicated they might be willing to permit at least teacher-led moments of silence.

Both justices repeatedly pressed Williams to explain why moments of silence for prayer or meditation, which Powell called "this little statute," violated the First Amendment's ban on governmental establishment of religion.

Williams acknowledged that a 1978 Alabama law calling for moments of silence for meditation was valid. That law was not challenged.

But the 1981 law, Williams said, which added the words "or prayer," went further and was an attempt to promote religion.

"The record is clear that there is no hindrance to religion under the old statute," Williams argued. The 1981 statute, he said, "suggests prayer is a preferred activity." Williams said the sponsor of the 1981 law testified that his purpose in proposing the change was to "return prayer to the Alabama schools."

John S. Baker, an attorney for the state of Alabama, argued that the law was a "common-sense accommodation" of religion that does not endorse religion, does not favor one religion over another and only "coerces" momentary silence.

But Justices Thurgood Marshall and John Paul Stevens repeatedly asked Baker and Deputy Solicitor General Paul Bator why the second statute was needed.

Baker said the 1981 law was required because people were "under the impression" that students didn't have a right to pray silently.

Bator replied that the inclusion of the word "prayer" in the second statute was purely informational and that there was "no constitutionally relevant difference between the first and second laws."

"Why do you need a statute?" Marshall asked. "Didn't students have a right to pray silently" before the 1981 law was passed?

Bator said they did, but that the 1981 law "enhances the opportunity to pray."

Stevens asked Williams to explain the practical difference between the two laws.

"It's the public perception," Williams said, pointing to "all the fanfare" that has accompanied this case.

A ruling is expected sometime this spring.