A federal judge here ruled yesterday that Victoria Churchville's bite into an apple on a subway platform - and subsequent false arrest by a Metro policeman - should be worth no more than $15,000, not the $30,000 a jury awarded her last month.

U.S. District Court Judge Howard F. Corcoran said there was "sufficient evidence for the jury" to find that Metro and one of its police officers, Thomas Hamlin, were liable for damages. But the judge said he had concluded "that the award of damages is grossly excessive and shocking to the conscience of the court.

"The damages awarded are in the opinion of this court so inordinately large as to constitute a miscarriage of justice," Corcoran said.

The judge said he reached that conclusion partly because Churchville, a journalist and energy policy analyst, "suffered no permanent physical injuries . . . [and] only momentary mental distress.

Corcoran gave Churchville until next Monday to accept the $15,000 award or said he would order a new trial to decide how much in damages she should receive.

Churchville was arrested Nov. 1, 1977, in the Eastern Market subway station and charged with consuming food on the subway and disorderly conduct.The disorderly conduct charge was later dropped and the other charge was dismissed. She contended that she munched on the apple on the station platform, where at the time it was legal to eat food, while Metro claimed she ate the apple in the train, where it was and still is against the law to eat food.