Russia today poured cold water on the idea of receiving help from the United States to complete a Siberian missile-tracking radar station in exchange for agreement on changes to the 1972 Anti-Ballistic Missile Treaty.

In a brief statement, the Foreign Ministry said "there are no grounds" for American newspaper reports about the U.S. offer of assistance that were published on Sunday. The ministry refused to elaborate, but Russian experts said the statement, while not an outright rejection, indicated that such a trade-off is unlikely.

The specialists said the Russian military remains adamantly opposed to any changes in the missile treaty. Although the United States and Russia have agreed to discuss possible changes in the treaty, the Russian specialists said formal negotiations have not started, and a deal may be a long way off.

"I have a very strong impression that the Russian military, and the Foreign Ministry as well, have taken this issue to heart, and they are determined to stand firm on ABM no matter what," said Paul Podvig, a researcher at the Center for Arms Control, Energy and Environmental Studies here. "The United States should understand what the situation is. There should be a clear understanding Russia is not at all happy with all this talk about changing the ABM treaty, and some in Russia seem to be willing to go as far as to pull out of the START I treaty."

That nuclear reduction pact is already in force. START II, which further slashes both countries' strategic arsenals, was signed in 1993 but never ratified by the Russian parliament. Both countries have expressed interest in moving to a third arms reduction treaty, START III, but it has not yet been negotiated.

Some arms control experts fear the entire arms reduction process could break down in a dispute over the Anti-Ballistic Missile treaty. Conservatives in Congress are arguing that the missile treaty is outdated and the United States must be ready to go it alone to build a national missile shield to protect against possible launches from North Korea and other nations.

The Clinton administration has said it will decide by next June whether to build the national missile defense system, which would require changes in the 1972 treaty, and has begun sounding out Russia on possible amendments. Russia has insisted that the treaty is a cornerstone of deterrence, and opposed any changes.

The treaty sharply limits the ability of either country to build ballistic missile defenses, in theory leaving both equally vulnerable to attack, which was viewed as a stabilizing factor during the Cold War.

Russia cannot compete technically or financially with the United States on missile defenses and its existing early warning system, composed of both radar and space-based satellites, is falling apart.

The U.S. offer was to help Russia complete a radar station near Irkutsk, and possibly others elsewhere, in exchange for support on treaty modifications. But one Russian specialist said the official reaction was that the proposal is "not sufficient" for changes in the treaty. Any treaty modifications will need to be accompanied by a START III agreement that reduces the numbers of nuclear warheads, this expert said.