Russian warplanes bombed secessionist Islamic fighters in the mountainous terrain of western Dagestan today as the president of neighboring Chechnya announced a month-long state of emergency, a move suggesting preparations for prolonged conflict.

Chechen President Aslan Maskhadov, a top military commander during Chechnya's two-year battle to secede from Russia in 1994-96, imposed the state of emergency starting tonight, including curfews and placing Chechen military units on high alert.

Chechnya borders Dagestan, where the Islamic fighters have seized several border villages, demanding that Russia abandon the northern Caucasus region, which it conquered two centuries ago. The rebels say they want to establish an Islamic state in Dagestan. In response to the incursion, Russia has launched an aerial bombardment of the guerrilla positions, and over the weekend also bombed inside Chechnya.

Chechnya has proclaimed its independence from Russia and, since the war ended, the border with Dagestan has crackled with tension, including kidnappings and murders. Chechen rebels have long considered expanding their fight with Russia to Dagestan, an ethnically diverse internal Russian republic. And in 1996, a raid by Chechen fighters into Dagestan led to one of the war's most intense battles at the border village of Pervomayskoye.

Maskhadov has said previously that he does not control the fighters now in Dagestan, but Shamil Basayev, the incursion leader, is a prominent Chechen commander, and news reports suggested that he has been calling for troops from Chechnya to reinforce his fighters. Basayev's top military commander, who is thought to be Jordanian or Saudi, goes by the nom de guerre Khattab.

Chechnya's announcement of a state of emergency reflected fears of a wider conflict. The Chechen security minister told Russian television that it was imposed "because the events of 1994 showed that we had not been ready for waging war." The presidential spokesman, Selim Abdulmuslimov, told Interfax news agency that the state of emergency was imposed following "top Russian officials' threats to use force against the Chechen republic."

Those threats continued today. The latest came from Gen. Anatoly Kvashnin, chief of the Russian general staff, who vowed in a Russian radio interview to "eliminate the rebels completely," and not simply push them back from Dagestan. "We are talking about destroying the rebels fully," he said.

However, the fighters are skilled combatants in the rugged mountains, where in recent years the demoralized and ill-equipped Russian troops have run into trouble.

Russian news reports said aerial attacks on the Islamic fighters were carried out through the night in Botlikh, a border town at the center of the fighting. Casualty reports were sketchy, but Russian officials said 21 fighters were killed in one attack, while one Russian militiaman was also killed, as well as two "volunteers."

The conflict in Dagestan began as Yeltsin fired his prime minister and appointed Vladimir Putin, a former KGB agent, to fill the seat. Putin, who faces a confirmation vote Monday in the lower house of parliament, is expected to win approval. But in advance of the voting he took a low-key approach to the conflict.

There has been speculation that Yeltsin or Putin may use the events in Dagestan as a pretext to impose a state of emergency and delay upcoming elections, but Putin said tonight in a television interview: "I believe there are no political conditions whatsoever" for doing so.

CAPTION: Gen. Anatoly Kvashnin, the Russian chief of general staff, vows to "eliminate" rebels in Dagestan.