MOSCOW, Nov. 10— As Russian troops spread out through the North Caucasus to enforce a state of emergency and quell a new outbreak of ethnic fighting, the leader of the break-away Chechen republic threatened today to take action unless the troops were withdrawn.

The threat by Dzhokhar Dudayev, a former Soviet Air Force general who declared his small ethnic homeland independent last year, added to the complexity and danger of the first conflict in Russia that President Boris N. Yeltsin has tried to resolve with force.

Last week Mr. Yeltsin imposed a state of emergency on North Ossetia and Ingushetia, in southern Russia, after Ingush commandos mounted raids to reclaim what they say are their ancestral lands in North Ossetia.

In a explaining the move, Mr. Yeltsin said, "Militant nationalists have unleashed a direct armed attack on the constitutional order of Russia, its security and territorial integrity." Death Toll Exceeds 250

Russian television said 133 Ossetians and 120 Ingush had been killed and 24 Russian servicemen wounded in the fighting. In addition, thousands of people reportedly fled into the mountains to escape the fighting.

The television report said the Russians moved today into Nazran, the capital of the Ingushetia region, with virtually no resistance. According to the Interfax news agency, part of their function was to block any shipment of arms from the Chechen region.

Ingushetia was merged with Chechenya in 1934 and the two later formed a republic within Russia. When the Chechen-Ingush republic declared independence last year, the two territories were not formally delineated.

Thus, when the Russian troops moved into Ingushetia, General Dudayev declared a violation of Chechen territory, despite the fact that the Ingush had declared themselves independent from Chechenya early this year.

"Russia should not forget where the borders of Chechenya are," Tass quoted him as saying. Otherwise, he warned, "both Nazran and Vladikavkaz will be blown sky-high." Vladikavkaz is the capital of North Ossetia.

General Dudayev also called for a "unified defense mobilization" to counter the Russians if they attack. Russia's Hesitancy

There was no telling whether General Dudayev would dare take on the Russian forces. A year ago, when the general declared independence, Mr. Yeltsin tried to dispatch troops, but had to pull them back under pressure from Chechen forces.

Since then, Moscow has left Chechen-Ingushetia alone, though it has not recognized its independence. Military specialists in Moscow note that last year's state of emergency failed in part because Russia did not yet have an army, only some Interior Ministry forces, and the Soviet Army remained neutral.

The new state of emergency has been supported by all major political forces in Moscow. It is to stay in force for a month, during which Moscow's representative is to search for a political settlement.

Mr. Yeltsin initially named Deputy Prime Minister Georgi Khizha as temporary administrator in the area, but he was replaced this month by Sergei Shakhrai, who was named Deputy Prime Minister for nationalities. There was no explanation for the change, nor for the abrupt resignation of the regional commander of internal forces, Col. Gen. Vasily Savin. The Heritage of Stalin

The Ingush-Ossetian clash is a legacy of Stalin's policy of simply deporting nationalities he did not trust. The predominantly Muslim Ingush were deported to Central Asia from the Prigorodny area of North Ossetia in 1944 for purportedly collaborating with the Nazis. They were allowed to return in 1957, but many of their lands remained in the hands of Ossetians.

The attacks by Ingush militants are intended to recover those lands.

About 100,000 Ingush live in Chechenya, Ingushetia and North Ossetia. There are about 400,000 Ossetians, who are Orthodox Christians; they live mostly in North Ossetia, which is in Russia, and South Ossetia, in Georgia.

The Caucasus, whose mountains are home to many tribes divided by language, religion and a history of feuding, has been a caldron of unrest since the collapse of Soviet authority.

Photo: A state of emergency has been imposed on North Ossetia and Ingushetia in southern Russia after Ingush commandos mounted raids to reclaim what they say are ancestral lands in North Ossetia. An Ingush refugee stood near Russian troops in Chermen. (Associated Press) Map showing the location of Chechenya.