President Mikhail Gorbachev called Monday for a national referendum to decide whether to hold the 15 Soviet republics together on the basis of his proposed Union Treaty.

"We must not let the union disintegrate. This would have a devastating effect on millions of people," he said in a state of the union message to the Congress of People's Deputies.Just after the 2,250-member congress convened Monday, a deputy who said she was ashamed that her country is accepting foreign food aid took to the podium and demanded Gorbachev's resignation.

The call for a no-confidence vote was rejected, but the political divisions that threaten the survival of the Soviet state were abundantly evident.

Nevertheless, Gorbachev said that by working together the Soviet people can overcome the crisis within 18 months.

"We have learned a lesson. We should not be panic-stricken," he said.

Gorbachev urged the congress to approve proposed constitutional amendments to strengthen the presidency, adding the post of vice president and replacing the 89-member Council of Ministers with a Cabinet of about 15 people.

Gorbachev aides say it is unlikely that Nikolai Ryzhkov, who heads the Council of Ministers and who is widely blamed for the failure of the nation's economic reform, will remain prime minister in the government reshuffle.

Before the congress opened in the Kremlin Monday, Gorbachev's aides indicated the Soviet leader wanted the body to endorse his Union Treaty.

Delegates from the republics of Lithuania and Armenia were boycotting the meeting, and lawmakers from Estonia and Latvia said they would not take part in discussions of the treaty.

"We must take strong measures to halt separatist nationalist actions," Gorbachev said in proposing the referendum. He said the results of the referendum in every republic "will be a final verdict." It was not clear when the referendum would be held or how it would be administered.

The congress, the country's highest lawmaking body, has the right to approve the proposed constitutional changes, but only the republics have the power to approve the proposed Union Treaty.

Gorbachev apparently sought to remove the decisionmaking power from separatist republics in favor of a direct vote.

Gorbachev's chief political rival, President Boris N. Yeltsin of the Russian republic, did attend the congress session. Gorbachev offered Yeltsin, who heads the largest, richest and most populous republic, the empty chair next to him on the podium, and the two men shook hands but did not speak.

Yeltsin is leading a movement among the 15 Soviet republics to wrest economic control from the central government.

In the call for a no-confidence vote, Sazhi Umalatova, a Communist Party member from the Chechen-Ongush Autonomous Republic in the Russian republic, accused the president of bringing "devastation, hunger, cold, blood, tears" to the people.

Fellow lawmakers sat in stunned silence and a national audience watched on live television as Umalatova accused Gorbachev of destroying the country.

Umalatova's call was rejected by a vote of 1,288 to 426 with 183 abstentions.