MOSCOW, SEPT. 3 -- Russian President Boris Yeltsin today urged all Soviet republics to become equal partners in a voluntary economic union and promised that Russia will never again act as a "big brother" to its smaller neighbors.

Yeltsin's comments to an emergency session of the full Soviet legislature were clearly designed to calm fears among other republics that Russian politicians might be tempted to build a greater Russian state on the ruins of the Soviet Union. The session is due to conclude Wednesday with a vote on transforming the once centralized country into a confederation of independent states.

"The Russian state has chosen democracy and freedom and will never be an empire or a big or little brother. It will be an equal among equals," Yeltsin told the congress of People's Deputies.

He said that "practically all" of the Soviet Union's 15 republics had agreed to participate in the new economic union, which appears to be closely modeled on the 12-nation European Community in Western Europe. Representatives from the Baltic republics of Lithuania and Estonia, which are both insisting on independence and refusing to join any kind of political union, took part in the preparatory work for a new economic agreement.

Soviet President Mikhail Gorbachev, in his address to the congress, said that republics would be allowed to choose their own level of association in a new, multi-tier Soviet Union. He said that the proposed new name of the country -- Union of Sovereign States -- would make it possible "to have a federative membership on some questions, confederative on others, and associate on yet others."

By offering the republics what amounts to "a la carte" membership in a reshaped Soviet Union, both Gorbachev and Yeltsin are attempting to salvage as much as they can from the wreckage of the world's first communist state. The core of the new union would be the republics that agreed to join a common defense and national security zone, control of which would remain largely with the central authorities.

Yeltsin, whose political authority has been enormously strengthened by his role in defeating last month's failed coup by Communist hard-liners, called for the preservation of "the union armed forces" and central control over the country's more than 25,000 nuclear warheads. He said that the giant Russian federation would guarantee preservation of the country's nuclear potential.

In an interview later with Cable News Network, Yeltsin said that strategic nuclear missiles now stationed in the Ukraine and Kazakh-stan would be transferred to Russian territory. He said a committee has been set up to control the nuclear weapons to ensure that they do not get into the hands of "ultra-left or ultra-right forces or terrorists."

After the failure of last month's coup, Russian officials said that the conspirators had deprived Gorbachev of the codes that allow the president to launch a nuclear missile attack in the event of war. The new Soviet defense minister, Marshal Yevgeny Shaposhnikov, has said that additional measures have since been taken to guard the security of nuclear codes and forestall any risk of accidental activation of missiles.

Although Yeltsin sought to reassure other republics that Russia respects the principle of "noninterference," he also reserved the right to "defend the interests of the people of Russia beyond the borders of the republic." At least 20 million ethnic Russians live in other republics, particularly the Ukraine, Kazakhstan, and the Baltic republics, and an equivalent number of non-Russians live in Russia.

Leaders of the republics reacted with alarm last week when the Russian president's press spokesman raised the possibility of reopening the territorial issue with republics that choose to leave the union. Yeltsin has since sought to back away from the statement, sending his vice president to the Ukraine and Kazakhstan in an attempt to repair the diplomatic damage.

Yeltsin sought today to consolidate his tactical alliance with Gorbachev, even though he sharply accused the Soviet president of encouraging the putschists earlier in the year and creating "a favorable soil for a revenge of the totalitarian system." He said that Gorbachev had become a "different man" after the coup, adding, "I personally trust Mikhail Sergeyevich Gorbachev much more now than, for example, three weeks ago."

Legislators will vote Wednesday on a package of proposed changes in the Soviet constitution that would establish a transitional authority to run the country prior to the signing of a new union treaty and elections to all-union bodies. The proposals have been endorsed by leaders of the main republics but have been attacked by conservative legislators as tantamount to an "unconstitutional coup."

In a concession to the conservatives, Gorbachev today modified a proposal for a new Council of Representatives made up of 20 deputies from each republic to take over as the supreme legislative authority. Instead he proposed a bicameral legislature. The higher, more powerful chamber is to be made up of delegates from the republics while the lower chamber will be drawn from the existing working parliament, or Supreme Soviet.

The new proposal, which avoids a formal dissolution of the Congress of People's Deputies, appears designed to avoid the danger of a revolt by rank-and-file deputies. Constitutional amendments must be approved by a two-thirds majority, difficult to reach even though most speakers in the debate clearly favored the changes.

Another resolution distributed to legislators today calls on the congress "to recognize acts of state sovereignty" adopted by Soviet republics on the basis of their existing borders. So far, 10 republics, led by the three Baltic states, have announced their independence.

The preoccupation with political issues has effectively overshadowed debate at the congress on the transition to a market economy. At a press conference today, Russian Prime Minister Ivan Silayev said that plans for economic reform are effectively on hold while the government takes emergency measures to prevent the economy from collapsing.

Silayev, who heads a committee of the republics on the economy that has assumed many of the powers of the central government, said he wants to avoid Polish-style "shock therapy" that could cause economic hardship to millions of people. His cautious approach appeared to be at odds with the much bolder policies advocated by his deputy, Grigory Yavlinsky, who advocates the immediate liberalization of the economy and relaxation of government controls.

The two men also disagree on the nature and scope of the new economic union. Silayev suggested that it should be open to former members of the East European trading organization Comecon, such as Poland, Czechoslovakia and Hungary, while Yavlinsky wants it to be restricted to the present 15 republics of the Soviet Union.

A draft proposal circulated by economist Stanislav Shatalin, who headed a working groupl of the republics, envisages a common community budget and customs zone as well as a coordinated monetary and taxation policy and a duty-free customs zone. Members would be allowed to introduce their own national currency but there would be a common banking system.

Yeltsin, in his interview with CNN, demanded the dismantling of the 12th Department of the KGB security police, which is responsible for electronic surveillance. He said that his phones had been tapped for the past five years and that "volumes and volumes of documents" tracing his life since 1989 had been found in the office of Yuri Boldin, Gorbachev's former chief of staff and one of the principal conspirators.

Yeltsin said that the 12th Department of the KGB had tapped at least 700 phones in the Moscow area alone on a regular basis.

In the southern republic of Georgia, meanwhile, demonstrators took to the streets for the second successive day to demand the resignation of nationalist President Zviad Gamsakhurdia. The demonstrators accuse Gamsakhurdia of authoritarian rule and failing to condemn last month's coup.

Soviet television tonight showed Georgian police beating demonstrators and firing into the air to disperse a demonstration Monday in the principal square of the capital, Tbilisi. Soviet Interior Minister Viktor Barannikov told the congress today that 20 people were injured in Monday's clashes.

In the southwestern republic of Moldavia, President Mircea Snegur said his government was taking control of the border with Romania and assuming command over Soviet frontier troops there. Moldavia, most of which was annexed by the Soviet Union from Romania in World War II, is attempting to follow the Baltic states to full independence.