Chechen President Dzhokar Dudayev told Interfax he expected Russia to send in three tank battalions, three airborne regiments and three infantry regiments.
Russian military officials denied planning an invasion and said some of the units mentioned by Dudayev, a former Soviet air force general, had been disbanded long ago.
With Russia openly backing the opposition, Chechnya, a tiny region of 1.2 million people, has grown increasingly tense in recent weeks.
Moscow has also warned it will take steps to protect Russian citizens in Chechnya, which declared independence in 1991.
The leaders of all 17 of Chechnya's clan, or teyps, held a congress Wednesday in Grozny, the capital, to decide what to do about Russia.
Nine of them called on Dudayev to impose martial law and mobilize Chechnya for war, Itar-Tass said.
Khasin Raduyev, spokesman for Dudayev, said the last such congress was held in the 19th century when Chechens were resisting Russian colonization.
"This is the first time in this century our country has faced the threat of aggression and the congress must decide what the people should do to repulse it," he told Itar-Tass.
Dudayev has frequently accused Russia of planning to invade and of backing his political enemies.
Alexander Starodubtsev, head of the region's Cossacks, said in a telephone interview that Dudayev supporters threatened to slaughter ethnic Russians in Chechnya if Moscow decides to invade.
According to some reports, the opposition has been trying to persuade Cossacks to join them.
Starodubtsev said he has advised Cossacks to stay out of the conflict between Dudayev and his foes.
Dudayev declared Chechnya's independence from Russia shortly after his election in 1991. Russia did nothing until recently to bring the republic back into the fold.
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