THERE IS NO WAY a judge or a jury can put an exact, or even approximate, value on an individual's First Amendment rights. But Judge William S. Bryant has had to try. He has decided that $750 is a reasonable sum to pay those whose rights were infringed on the steps of the Capitol eight years ago.

The trouble came a few days after the May Day demonstration of 1971 that almost brought life in the city to a halt. About 1,200 demonstrators were arrested on Capitol Hill after police broke up a rally that Rep. Ronald V. Dellums (D-Calif.) was addressing.

In 1975, the demonstrators successfully made their point in court that the arrests were illegal and that their rights to free speech and freedom of assembly had been violated. A jury awarded damages that averaged about $1,000 per demonstrator for the injuries caused by the false arrests. The jury also decided that each demonstrator should receive $7,500 for the loss of First Amendment rights. After being told by the Court of Appeals that $7,500 was "extravagant," Judge Bryant settled on $750, considerably more than the District government wanted to pay and considerably less than the demonstrators' lawyers thought it should.

The point of the litigation that flowed from the entire May Day episode was to establish the rights of both the demonstrators and the city in future demonstrations. That has been a sobering experience for both sides, as the courts have spelled out in more detail the point at which the exercise of First Amendment rights turns into conduct a community is free to suppress. The monetary damages are an afterthought, and by setting them at $750 Judge Bryant has picked an amount large enough to let the demonstrators know the police acted illegally but not so high as to punish unduly the taxpayers for errors made by public officials during a truly trying period in this city's history.