Ukraine Agrees to Join Economic Union : Soviet Union: Richest republic becomes the 10th to approve the new pact. But nationalists predict that it will be rejected in the Dec. 1 referendum.

The Ukrainian Parliament voted after a fierce debate Wednesday to sign the treaty establishing an economic common market on the ruins of the Soviet Union.

But the deputies said the pact will have to be ratified and a number of supporting agreements approved before the Ukraine, the richest and most populous republic after the Russian Federation, fully joins the “economic community.”

Almost immediately after the 236-96 vote here, Prime Minister Vitold Fokin signed the accord in a Kremlin ceremony in Moscow. That brought to 10 the number of republics that have agreed to establish the new economic union. Moldova, the former Moldavia, also signed the treaty on Wednesday.

But Ukrainian nationalist leaders predicted the accord’s ultimate rejection here after the Dec. 1 referendum on the republic’s independence.

“I do not think the Parliament will ratify it--if this Parliament exists at the time the question arises,” said Ivan Drach, leader of the Rukh, the opposition nationalist movement. “This was a Pyrrhic victory for Fokin.”

With the Parliament adjourned until Dec. 3, the question of ratification will arise only after the referendum and the election, also on Dec. 1, of a president. New parliamentary elections might be called if Ukrainians vote, as expected, for independence.

“Without ratification, Fokin’s signature has no legal effect,” Deputy Serhij Holovatij said.

With the referendum--pivotal not only for the Ukraine but also for the whole Soviet Union--only weeks away, the republic was clearly hedging its bets, taking steps to remain in the new economic union but leaving itself the chance to break away.

Yet, the Ukraine’s participation in the economic community being forged by Soviet President Mikhail S. Gorbachev is regarded as essential for its success and for the “Union of Sovereign States,” a loosely structured confederation of former Soviet republics that Gorbachev also hopes to establish.

All but two of the 12 remaining Soviet republics have now signed the economic pact--the holdouts being the southern republics of Georgia and Azerbaijan. The three Baltic states of Estonia, Latvia and Lithuania have refused to join the pact but are expected to negotiate close commercial ties.

Wealthy and fertile, the Ukraine has a population of 52 million in a territory the size of France; before the collapse of the Soviet economy, it accounted for about a quarter of the country’s industrial and agricultural production.

For weeks, Fokin argued hard for the treaty as essential to halt the Ukraine’s economic decline because the delivery of goods from other republics, notably Russia, was slowing and even stopping.

But after studying the document all night, none of the 14 legislative commissions that reported to Parliament on Wednesday urged that the Ukraine sign the treaty in its present form.

In Moscow, Leonid M. Kravchuk, chairman of the Ukrainian Parliament and a leading candidate for president, met with Russian Federation President Boris N. Yeltsin to reach an accord between the two republics and between them and the central authorities.

Russia and the Ukraine had agreed, they said, on the necessity for joint control of nuclear weapons--a matter of dispute until now--and Russia recognized the Ukraine’s right to establish its own conventional armed forces.

Special correspondent Mary Mycio reported from Kiev and Times staff writer Michael Parks from Moscow. Viktor K. Grebenshikov, a reporter in The Times’ Moscow Bureau, contributed to this report.