Six Czechoslovak human rights activists were convicted of "subversion of the state" tonight by a Prague court, which sentenced five of them to prison terms ranging up to five years.

The trial, which ended two days earlier than expected, was immediately denounced by the U.S. Helsinki Watch Committee as "further proof of the pattern of human rights abuses" in Eastern Europe.

"We call on the governments and citizens of all signatories of the 35-nation Helsinki conference on European security and cooperation to join with us in our efforts to obtain the release of those imprisoned Czecvhoslovak activists," the committee said in a statement.

The State Department had earlier called in the Czechoslovak ambassador in Washington to protest "in strongest possible terms" against the trial.

The official Czechoslovak news agency Ceteka said playwright Vaclav Havel, 43, was sentenced to 4 1/2 years and economist Peter Uhl, 38, was given five years at the end of two-day proceedings that ended Czechoslovakia's biggest show trial since 1972.

The sentences were first disclosed by dissident sources and later confirmed by the official agency. Lesser sentences were given to the four other defendants.

The sources said Vaclav Benda, 33, a former spokesman for the Charter 77 human rights movement, was sentenced to four years; former television commentator Jiri Dienstbier, 42, and Otta Bednarova, 54, a journalist were given three-year sentences and Dana Nemcova, a Roman Catholic dissident and mother of seven children, was given a two-year sentence that was suspended.

All of the sentences were disclosed at the conclusion of the second day of proceedings, which began at 8 a.m. and continued until after 9 p.m.

An estimated 50 policemen took up positions around the courthouse before the verdicts were delivered and reporters saw other police in patrol cars parked on darkended side streets.

Authorities had barred journalists and supporters of the activists from attending the trial.

Government prosecutors had asked for maximum penalties of 6 1/2-to-10 years for Havel, Uhl and Benda, according to the sources.

Medium-range sentences of up to 6 1/2 years were said to have been sought for Bednarova and Dienstbier and a suspended sentence for Nemcova.

The defendants are alleged to be founders of what the government claims was an illegal group formed to aid dissidents and help foreigners make hostile propaganda against the state.

They are among 10 people arrested May 29 in raids on the so-called Committee for the Defense of the Unjustly Prosecuted. The other four are still in jail awaiting a trial date.

All but a few members of the defendants' families were barred from the heavily guarded courtroom building on a downtown Prague intersection.

Uniformed police occupied nearby street corners where supporters of the dissidents had gathered in small numbers the day before. They, family members and Western newsmen were placed under what appeared to be intentionally obvious plainclothes police surveillance.

The trial continued to draw stinging criticism today from abroad.

Italian President Sandro Pertini joined a growing list of foreign critics of the trial, saying it "shocks the Italian people."

Among other Western political protests against the trial was one from the French Communist Party.

And European Parliament President Simone Veil said in Strasbourg, France, that she would ask Common Market foreign ministers to intercede for the defendants.

A motion protesting the trial was introduced at the Strasbourg assembly by exile Czech dissident Jiri Pelikan, now an Italian delegate to the Parliament.

Accusations in the Prague trial charge Pelikan is one of the dissidents abroad whose activities are directed by the U.S. Central Intelligence Agency and that his efforts were aided by material from the defendants.

Government officials in Prague claimed today they could provide no information on the trial. Reporters inquiring at the court building were told information was available at the Foreign Ministry, but officials there said none was available.

Sources said judges refused defense protests over the hurried proceedings. Similar protests were lodged unsuccessfully yesterday when the opening day proceedings dragged out over a dozen hours with an hour out for lunch.