MOSCOW, JULY 24 -- A top aide to Soviet President Mikhail Gorbachev said today that the diverse and restless republics that make up the Soviet Union would probably agree by December on a revised treaty of union granting them greater autonomy from the Kremlin.

But the aide, Grigori Revenko, said Gorbachev told advisers on Friday that he believed eight key areas, including defense, currency, energy and transport, would have to remain under central control.

Gorbachev's position seemed certain to stir opposition in the 15 republics, 10 of which have already adopted sovereignty declarations proclaiming the supremacy of their laws over Soviet legislation.

The Ukraine, the second-largest republic after Russia, took the most radical course, claiming a right to create its own security forces, currency and banking system and declaring its intention to become a neutral state. The giant Russian republic, led by populist President Boris Yeltsin, has claimed ownership of all natural resources and financial institutions on its territory and has put forth a program of property privatization independent of the Kremlin.

"You've got to look at this realistically," Revenko told reporters when asked about such declarations. "Today, many serious documents are imbued with the atmosphere of a political meeting. They are not properly thought out. It's a position adopted for negotiations."

Asked what would happen if Yeltsin tried to take control of Russia's vast oil and gas reserves, Revenko hinted he thought the central government was in a strong position. "What would happen if {the Kremlin} refused Yeltsin 30 million tons of grain he needed?" he replied.

Revenko said that under the Kremlin's shift to a market economy, oil and gas eventually would not be controlled by governments, but by independent fuel enterprises.