Moldavia's deputies walked out of the fourth Congress of People's Deputies Tuesday, the sixth Soviet republic that will not take part in the entire 10-day conclave in a mounting affront to Mikhail Gorbachev.

In a further setback to Gorbachev's plans for the 15 republics to sign a new union treaty, officials from the breakaway Baltic republics and other leaders rejected his proposal for a national referendum on the future of the Soviet Union.Estonian President Arnold Ruutel, whose republic has declared independence from the Soviet Union along with the other two Baltic states, told the Congress the Baltics instead favor a normalization of "interstate relations" with Moscow.

"Estonia did not hold any referendums when it was taken over by the Soviet Union in 1940," Ruutel said. "The question of holding a referendum now is illegitimate."

He later told United Press International in answer to a question: "We do not intend to hold such a referendum, because when we came into the Soviet Union in 1940 there was no referendum."

The problems of ethnic strife intruded on the second day of the Congress, causing Moldavia to join Estonia, Latvia, Lithuania, Georgia, and Armenia in either full or partial boycotts of the conclave.

Moldavia's Deputy Prime Minister Konstantin Oborok complained that the Congress ignored two requests by the Moldavian deputies to discuss the internal ethnic problems tearing their republic apart.

Oborok explained that he objected to the presence at the Congress of deputies from the Moslem Gagauz region and Russian-speaking southern area that have declared themselves independent in acts declared invalid by Moldavia.

"Their presence deprives the Moldavian deputies of their right to participate in the Congress," Oborok said, and the Moldavian nationalists left the hall.

The proposal for a vote on whether republics could secede from the Soviet Union and Gorbachev's request for more presidential power to deal with the economic crisis in the country came under renewed sharp attack Tuesday at the Congress.

"It is a useless thing," Russian republic leader Boris Yeltsin said of Gorbachev's proposal. "The republics have to agree among themselves. No one must dictate to us."

Newly elected nationalist-controlled parliaments in Estonia, Latvia and Lithuania passed declarations of independence earlier this year, and all but one of the other republics have approved milder sovereignty proclamations.

The three Baltic states and the Transcaucasian republic of Georgia have said in recent weeks that they will not sign a treaty subordinating themselves to Moscow. Nationalist sentiment is also strong in Armenia and Moldavia, where tens of thousands of people demonstrated Sunday against joining a new union.