Still, owing to its legacy of Soviet bases to support any ground war to the west, the military is poorly positioned to counter an attack from the east, according to Ruslan Pukhov, the director of the Center for Analysis of Strategies and Technologies, a military research institution in Moscow. The thin military presence in the east complicates any response if Russia chooses, for instance, to back pro-Russian activists who have reportedly seized administrative buildings in Kharkiv, in eastern Ukraine.

According to its website, the Ukrainian military has a total of 130,000 people under arms, with reserves of some one million. While conscription recently ended, it remains a largely conscript army. Ukraine has partially reformed its military since the Soviet days, when it was organized in large-scale divisions. It is now organized on the more flexible brigade system and has been reducing the size of its military forces, but it is underfunded with a lot of outdated hardware.

Ukraine had accomplished some military reform with NATO advice, but since President Yanukovych said that Ukraine was not interested in full NATO membership, cooperation has lagged, the NATO official said. Ukraine has, however, taken part in some military exercises with NATO, contribute some troops to NATO’s response force and helped in a small way in Libya.

In general, the Ukrainians are considered to have excellent home-produced tanks, but have also relied in part on the BMP-1, an infantry fighting vehicle that is a combined armored personnel carrier and light tank dating from the early 1970s. Ukrainian air defenses, all produced in Russia and a generation behind, are considered weak.

Mr. Pukhov, at the military research institution in Moscow, said that the Ukrainian military inherited a vast supply of legacy weapons from three Soviet military districts. “But 22 years have gone by during a state of near continuous economic decline and the Ukrainian military has received practically no new equipment,” he said. “Now the force is somewhat pathetic.”

He said the forces in Crimea were there less to defend Crimea than to prevent Crimean Tatar separatism and even more unofficially, Russian separatism. During Ukraine’s recent military reforms, contract soldiers were allowed to serve near their homes, meaning that many of the junior officer corps on the peninsula are also residents of Crimea, which is majority ethnic-Russian, so they are possibly more pro-Russian in their views.

On Saturday, Pyotr N. Mekhet, a reserve colonel offered a top position in Ukraine’s Ministry of Defense, said the government should mobilize, or “the people will form militias,” suggesting a partisan movement could emerge.