MOSCOW, NOV. 17 -- Soviet authorities are mounting an all-out bid to thwart a nationalistic demonstration against Soviet rule in Latvia, which is scheduled to take place Wednesday in that Baltic republic, according to activists there.

In honor of Latvians' national day, activists have called for a protest against Soviet rule, to consist of laying flowers at the foot of the freedom monument in the center of Riga, the republic's capital.

Officials there, using the local news media, have warned against participation in the protest and also have attacked U.S. congressmen for their support of the celebration of Latvia's independence day.

"They are getting prepared, bringing in brigades, broadcasting lies about the demonstrations," activist Georg Rubenis said from Riga in a telephone interview tonight. "They are prepared for a major repression. I don't know what is going to happen."

The drive by Soviet authorities to suppress the protests represents a turnabout from last summer, when demonstrations against Soviet rule in Riga, drawing thousands of Latvians, were allowed to take place without serious obstruction. Soviet authorities also permitted Crimean Tatars' protests in Moscow to demand a return to their homeland.

Today, in a television broadcast one day before the protest is to take place, state-controlled Latvian television broadcast an appeal from a Latvian dissident, recently released from prison, for locals to avoid joining the demonstration.

Linard Gratins, who was head of the Riga-based human rights group Helsinki '86 before he was jailed earlier this year, also said that had he been free during a major protest in Riga earlier this year he would not have taken part.

In a broadcast last week, Kim Philby, the British double agent who defected to the Soviet Union in the 1960s, told Latvians that western intelligence uses emigre organizations to stir unrest in the Soviet Union.

Official Latvian historian Visuaris Miller, in an interview released here today by the official Soviet news agency Tass, protested a recent U.S. congressional resolution for Latvian independence as "overtly provocative."

A group of Communist Party officials from Latvia yesterday sought to issue a protest at the American Embassy against the congressional resolution calling for an independent Latvia.

Ambassador Jack Matlock declined to meet with the Latvian officials, however, in keeping with U.S. policy against meeting with party officials from the Baltic republics. The United States does not recognize Latvia, Lithuania or Estonia as part of the Soviet Union and refuses direct contact with officials from them as a protest against Soviet rule in the region.

The U.S. Congress passed a resolution recently protesting Soviet rule in Latvia, which resulted from a 1939 pact between the Soviet Union and Nazi Germany that ceded to Moscow territorial control over the three republics. Germany agreed not to enter into war against the Soviet Union, but proceeded to do so. Reaction to the congressional resolution, Latvian official Carl Rutenberg told Tass, was "anger and indignation."

"The resolution of the American Congress is a gross interference in the internal affairs of a Soviet republic," Latvian official Andris Berzins was quoted as telling Tass.

"One would like to believe that common sense and new political thinking will prevail in the U.S.A. and the Congress will discard the notorious resolution on the 'the Baltic question,' which, incidently, has been resolved by history in a final way," Berzins added.

When the Tass dispatch was broadcast on Latvian television, reporting the officials' attempt to meeting with Matlock and their response to the U.S. congressional resolution, residents of Riga reacted promptly, according to Latvian activist Rubenis. "They laughed," he said in an interview.