MOSCOW -- On Monday, President Mikhail S. Gorbachev told the Fourth Congress of People's Deputies that "the country and the people are becoming increasingly convinced that it is vitally important to preserve" the Soviet Union on the basis of his proposed union treaty.
Yesterday, evidence to support his thesis was hard to come by:
* Latvian officials charged that three explosions in Riga early in the day were staged by communist and military hard-liners as a prelude to a military takeover to block Latvian independence. The blasts, in which no one was hurt, occurred within minutes of one another at a Communist Party building, a military office and
near a statue of Lenin.
* Estonian President Arnold Ruutel ruled out for his republic any referendum on the future of the union, as proposed by Mr. Gorbachev. When Josef V. Stalin annexed the three Baltic republics in 1940, Mr. Ruutel acidly noted, there had been no referendum in Estonia.
* Nearly the entire delegation from Moldova walked out of the Congress, joining deputies from Armenia and Lithuania, who chose not to send delegations in the first place. The Moldovans said there was no chance that the republic would sign the union treaty.
* The president of Uzbekistan, Islam A. Karimov, joined neighboring Kazakhstan's rejection of the draft treaty, saying it should be produced by the republics, not handed down
by the Kremlin leadership. Even traditional Central Asia, where little resistance to the treaty was expected, was putting up a fight.
* The head of the Siberian military district said draft resistance in the republics would cut the Soviet army's planned troop strength by at least 15 percent this year. "Soldiers from various republics today ask the question: Do we have to serve in the armed forces if there's not going to be a union?" he said.
Mr. Gorbachev's vision of a national referendum to rally support for a renewed union, followed swiftly by a new treaty uniting the 15 Soviet republics, increasingly seemed a mirage, observers said.
Republican leaders, most of them representing the nationalist forces brought to power by this year's democratic elections, demanded real sovereignty or outright independence. But many conservative deputies representing old power structures echoed Mr. Gorbachev's call for "order" above all.
The resulting confrontation seems sharpest at the moment in Latvia, a heavily militarized republic where just 53 percent of the population is ethnic Latvian. The Soviet army's refusal to obey Latvian laws last month provoked the parliament to threaten a cutoff of food and power to military bases, and relations have gone downhill since then.
The size of the non-Latvian population and the prominence of the Communist-military alliance in Latvia makes the republic a tempting target for conservatives who want to challenge the nationalists.
Ilmar O. Bisers, first deputy prime minister of Latvia, said the Soviet government was threatening the republic with either an economic blockade or direct presidential rule by Mr. Gorbachev if it refuses to sign the union treaty. In this context, yesterday's explosions were interpreted by Latvian leaders as a provocation. They followed similar, small blasts last week at another Communist Party building and republican KGB headquarters in Riga.
"Watching the actions of the provocateurs, their scenario is quite clear and its final aim is for the center [Moscow] to proclaim a state of emergency and the introduction of presidential rule in the republic," Latvian leaders said in a statement.
Despite the overwhelmingly negative reaction from republican representatives to Mr. Gorbachev's appeals, he stuck to his position on a referendum on the future union. During a break in the proceedings, he also defended his proposal for a second referendum on private land ownership, though many deputies noted that the giant Russian Federation already has authorized such ownership and is hardly likely to consent to a referendum.
"I will insist that we hold these two referenda, and I hope the lawmakers will support me," he said.
About the only development running counter to the trend toward conflict and disintegration yesterday was the signing of a treaty between the Russian Federation and Byelorussia.
Again, two republics agreed to establish direct economic and political relations, bypassing the central government.
Russian leader Boris N. Yeltsin, who signed the treaty, has said only direct ties between republics can become the basis for a strong union. His view has received considerable support at the congress.
Yesterday, asked whether he would speak, Mr. Yeltsin told a reporter that his opinion of Mr. Gorbachev's Monday speech was so low that he may refrain from speaking at the congress to prevent from worsening relations between the Kremlin and the republics.