MOSCOW, JUNE 21 -- Nationalists in the Soviet Baltic republic of Latvia defied authorities by staging an unauthorized gathering to mark Joseph Stalin's deportation of thousands of Latvians to labor camps in 1941, according to an official newspaper that arrived here today.

The nationalists, some of whom belong to a Latvian human rights group called Helsinki-86, laid flowers at the Monument to Freedom in the republic's capital, Riga, the Latvian Communist Party daily Sovietskaya Latvia said.

In its Thursday edition, the newspaper said the incident occurred June 14. It did not estimate how many people took part in the action but said police had not interfered.

{Members of Latvian emigre groups in the United States who spoke to people in Riga by telephone reported on the march last week. They quoted Rolands Silaraups, an organizer of the demonstration, as saying as many as 5,000 demonstrators and bystanders had gathered in the city's central square.}

Unofficial sources in Moscow confirmed that the Helsinki-86 group had been involved. They said police had videotaped those who took part but had taken no other action.

The sources said some people called for the release of jailed Latvian political dissenters.

The incident was the latest demonstration of nationalism to be reported in the official press. Street riots flared in the Central Asian republic of Kazakhstan last December after an ethnic Russian was appointed as the republic's new party leader.

Disturbances involving local and foreign students have been reported in the Central Asian republics of Tadzhikistan and Kirghizia, and fights between people of different nationalities have been reported in Moldavia.

Sovietskaya Latvia published a letter on the incident in Riga from a reader, A. Libert, who said: "Individual people behaved unworthily, violated public order, and openly talked at length about bourgeois nationalist ideals alien to us."

Latvia and two neighboring Baltic republics, Estonia and Lithuania, were forcibly incorporated into the Soviet Union in 1940. Western historians estimate that 14,000 Latvians as well as thousands of other Balts were deported.

Sovietskaya Latvia accused U.S.-supported radio stations of inspiring the incident in Riga but said it was wrong to view as anti-Soviet an action aimed at marking the memory of innocent victims.

"The indelicate choice made by individuals who were clearly prompted by subversive radio broadcasts, to lay flowers at the Monument to Freedom on June 14, can hardly be regarded as an attack on the socialist system," the newspaper said.