KIEV, Ukraine — On the eve of a key summit, Ukrainian officials Thursday scorned attempts to strengthen the Commonwealth of Independent States and adamantly refused to give up legal claims to nuclear weapons remaining on Ukraine's soil.

Breaking again with the 10 other Commonwealth members, Ukraine indicated it would not sign a proposed charter for the amorphous grouping that arose on former Soviet territory.

"Ukraine cannot accept the transition of the C.I.S. into a new supranational structure," said Anton Buteiko, chief foreign policy adviser to Ukrainian President Leonid Kravchuk. "It would be little more than a revival of the Soviet Union."

In Minsk, the capital of Belarus and the Commonwealth where Commonwealth defense ministers gathered for a preliminary meeting, Deputy Ukrainian Defense Minister Ivan Bizhan said that, although nuclear weapons left in Ukraine remain under Commonwealth operative control, "they should remain under the administrative jurisdiction of Ukraine."

That position has Commonwealth military commanders openly concerned that confusion over ownership of the 176 nuclear missiles left in Ukraine could lead to dangerous instability.

Marshal Yevgeny I. Shaposhnikov, the Commonwealth's top armed forces commander, complained this week that the nuclear weapons in Ukraine are essentially without an owner. "At present, there are weapons, they are functioning, but there is no jurisdiction of any state over them," he told reporters, saying the missiles' legal limbo has created problems for the Russian experts needed to service them.

But Shaposhnikov made it clear for the first time that Russia has total physical control over any nuclear launch. Ukraine has the theoretical right to veto a launch from its territory, he said, but "that is only an organizational veto, not a technical one."

Shaposhnikov and Russian defense officials are expected to press Ukraine on the issue of nuclear ownership at today's summit.

Ukraine is expected to resist. "Everything that is located in Ukraine . . . is the indisputable property of Ukraine," Bizhan said.

Once again, the Commonwealth summit appeared likely to end in deadlock between Ukraine and Russia.

Designed as a "civilized divorce mechanism" for former Soviet republics, the Commonwealth summits have aimed to support international trade in the region and foster political cooperation. But many of the 11 member states have reached a dangerous crossroads, with internal dissent rising and a cluster of wars undermining their stability.