Russian troops seeking to put down a revolt in Dagestan suffered their worst losses yet in a failed attempt to storm a mountain village controlled by Islamic militants, Russian officials said today. Russian commanders said they will not attempt another direct assault for fear of heavy casualties.

Russian troops have lost 18 soldiers in the past 24 hours, the officials said, during the effort to storm Tando, a remote village held by the Islamic separatists in western Dagestan, along the border with Chechnya. That brought the total Russian toll to 40 dead and 160 wounded in a conflict that has lasted nearly two weeks, according to the deputy interior minister, Lt. Gen. Igor Zubov.

He said 400 to 500 rebels have been killed, but they have denied such high losses.

The battle for Tando came after the area had been heavily bombarded in recent days. But a Russian newspaper, Kommersant, said the Russian soldiers were surprised when the separatists emerged from basements and caves amid the rubble. Paratroopers were hit as they landed; three Russian helicopters were downed. Zubov said about 400 fighters remain in Tando.

The conflict began when a feared Chechen field commander, Shamil Basayev, led bands of his fighters over the border into Dagestan and vowed to establish an Islamic state in the multi-ethnic Russian republic on the Caspian Sea. Chechnya fought a bitter secessionist war with Russia in 1994-96, but President Aslan Maskhadov has denied that he approved the latest military foray into Dagestan.

For days, the Russian military has been saying it would soon have the situation under control. But after the Tando defeat, Russian commanders were talking about switching tactics and avoiding a costly head-on assault.

"They could be taken by direct assault, but it would bring big losses," said Zubov. "Therefore . . . I must say we have decided to make sure our losses come to a minimum.

"The peculiarity of the local terrain is very difficult, the veterans are saying that even in Afghanistan we have not seen anything like it."

He said that artillery and airstrikes, which have been Russia's primary tactics since the outbreak, have failed to dislodge the rebels, who are believed still to control the villages of Ansalta, Rakhata, Tando, Shadroda, Ashino and Zibarkhali.

Instead of storming villages where the fighters are entrenched, Zubov said the Russian troops instead will try to cut the rebels' retreat routes back into Chechnya and destroy their communications and supply lines.