New Yeltsin Challenge to Gorbachev : Soviet Union: The Russian Federation president threatens a referendum on greater central authority.

Populist politician Boris N. Yeltsin, locked in a fight with Soviet President Mikhail S. Gorbachev over how to share power, threatened Monday to hold a referendum to determine whether the Russian people really want to grant the increasingly unpopular Gorbachev more authority.

In his first public statement on Gorbachev’s proposals for sweeping government reform, the Russian Federation president said he was frankly “disappointed” because they would vest too much power in the Moscow-based bureaucracy and would ignore suggestions he and leaders of the other Soviet republics had made.

Significantly, however, Yeltsin did not reject out of hand the recommendations Gorbachev made Saturday in the national legislature, the Supreme Soviet, and said he needed to study them further.

“My position on them is not simple,” Yeltsin explained.

But in his remarks to Ukrainian lawmakers in Kiev, the Russian leader did lambaste Gorbachev for “striving to make the center omnipotent once again” and likened the president’s program to how former Prime Minister Nikita S. Khrushchev had tried to transform the country.

“When the center decided to centralize everything, the reforms ended,” Yeltsin said.

What took the strapping Siberian to Kiev was an event epitomizing the centrifugal forces now tearing at the Soviet Union, and which Gorbachev is trying simultaneously to channel and combat.

In a protocol-packed ritual befitting leaders of two independent states, Yeltsin and Ukrainian President Leonid M. Kravchuk signed a treaty pledging mutual cooperation between their republics in trade, culture, health protection, ecology and even “defense and security.”

Alarmed that many of his orders now go unfulfilled by the government apparatus, Gorbachev has proposed a revamping of the executive branch to give him hands-on control of the Cabinet, a function now exercised by Prime Minister Nikolai I. Ryzhkov. But Gorbachev also is offering Yeltsin and the other republic leaders a greater share in Kremlin policy-making by converting a consultative body they sit on into the supreme organ of power.

Yeltsin, whose anti-Establishment and egalitarian views have made him the most popular politician in the country, said in Kiev that he is ready to take Gorbachev’s proposal to the Russian people, in the form of a referendum, to see what the citizenry wants.

If the information gleaned by Soviet public opinion polls, still in their infancy, can be believed, any referendum on Gorbachev would probably be a political disaster for the 59-year-old Kremlin leader--and something he would want to avoid, perhaps even at the price of assenting to some of Yeltsin’s demands.

As some of the country’s biggest cities impose food rationing and even humble goods like matches become rare in places, Gorbachev’s popularity rating has plummeted, apparently to its lowest point ever.

For example, only 21% of the people polled last month in 10 of the country’s regions said they now “fully approve” of Gorbachev’s activity, the Moscow-based All-Union Center for the Study of Public Opinion reported. The approval rating last December was as high as 52%.

“If the president were to be democratically elected today, to judge by numerous opinion polls, Mikhail Gorbachev would probably be unable to confirm his right to the country’s leadership,” the liberal weekly Moscow News said last week.

Yeltsin also said he is ready to ask the voters in the Russian Federation, which has half of the country’s population, to express their confidence or lack of it in Ryzhkov’s government.

Yeltsin wants the 61-year-old technocrat thrown out of office and replaced with a “national unity” government he says would be more favorable to economic reform.

With the increasingly restive Soviet republics demanding more and more autonomy, there have been previous agreements by their leaders--for example, by the heads of the five Central Asian republics--but nothing as potentially far-reaching as the Russian-Ukrainian accord.

Between them, the two Slavic lands--the Soviet Union’s most populous and richest territorial units--have more than 200 million people and almost twice the land mass of the United States. With their vast natural resources, farm lands and industries, Russia and the Ukraine account for 85% of Soviet consumer goods production.

Seated at a table decorated with the flags of their republics, Yeltsin and Kravchuk initialed the eight-page pact. As Izvestia, the Soviet government newspaper, noted, the treaty significantly makes no reference to the Soviet constitution or the 1922 agreement that created the Soviet Union, but refers instead to “sovereign” Russia and the Ukraine.

In an interview with Soviet television, Yeltsin said that such direct ties between the republics, bypassing the institutions of the central government, are the best way to create a new Soviet Union.

“This process is going from the bottom up. . . . We must proceed gradually from here,” he said, implicitly criticizing Gorbachev’s attempts to spearhead the conclusion of a new union treaty.