Boris Yeltsin, president of the republic of Russia, threatened not to sign a proposed unity pact with the central government unless his republic is given substantial control over its own natural resources, including diamonds and oil.

The threat Wednesday, following refusals by other of the Soviet Union's 15 republics, could spell trouble for Soviet President Mikhail Gorbachev's plans to reorganize his nation.Yeltsin also criticized Gorbachev's proposals to expand his own powers, calling them "not quite clear or consistent" and urging a plebiscite on the matter.

"If we want to know exactly whether the public wants Mikhail Gorbachev's presidential powers in full or not, we have to hold a national referendum," Yeltsin said. "Russia has a law on referendums and we can hold one."

Yeltsin, increasing the stakes in his growing power struggle with Gorbachev, set two conditions for signing a "union treaty" that is to be the legal basis of a reconstituted country.

"Russia will sign the new union treaty if it is going to have actual sovereignty, if its (June) declaration of sovereignty is officially recognized by the Supreme Soviet or the president.

"The second condition is an agreement between the governments of Russia and the Soviet Union on the separation of functions," said Yeltsin. "Questions of property, including foreign currency, diamonds, precious metals, oil, gas and so on, must be settled. Russia will not sign the union treaty before these issues are settled."

Gorbachev promised local governments greater autonomy in the reformed "Union of Sovereign Soviet Republics" under a new pact leaders of the 15 republics would voluntarily sign, replacing the 1922 treaty by which the Soviet Union came into existence.

The Baltic republics of Estonia, Latvia and Lithuania declared independence earlier this year and say they will not sign the pact. The Transcaucasian republic of Georgia said it would not sign after nationalists gained control of the Tbilisi legislature in elections last month.

But Yeltsin's statement was his first indication that the dominant Russian Federation might not enter into the agreement, a refusal that could spell trouble for the Soviet Union as a viable country.