* Ukraine's new leaders face challenge in Crimea
* Many ethnic Russians want more independence
* Some favour secession, form militias
By Alissa de Carbonnel
SEVASTOPOL, Ukraine, Feb 28 (Reuters) - Flying the Russian flag, men in combat fatigues wave down cars at a roadblock made of plywood and tyres outside this port city in Ukraine's southern region of Crimea that dates from Tsarist times.
They are ethnic Russians intent on defending Sevastopol against people they regard as Ukrainian nationalists who they fear may arrive from the capital Kiev to impose their rule after ousting President Viktor Yanukovich.
"We don't want to be ruled by fascists," said Oleg Golovan, a retired Russian military officer who is in charge of the checkpoint about 20 km (12 miles) outside the city.
The leaders and protesters in Kiev who brought down Yanukovich a week ago are heroes in the capital and the West, and have been grudgingly accepted in mainly Russian-speaking areas in the east.
In rimea, on the other hand, they are compared to the nationalist militias sometimes accused of siding with Nazi troops against Soviet forces during World War Two.
That perception has inflamed secessionist yearnings on the Black Sea peninsula, the only region in Ukraine where ethnic Russians are as majority.
In Sevastopol, where Russia's Black Sea fleet has a base, residents speak unabashedly of wanting Crimea to return to Russia's fold, 60 years after Soviet communist leader Nikita Khrushchev gifted the territory to then Soviet Ukraine.
Crowds rally daily in front of city hall, and voted with roars of approval this week for Russian citizen, Alexei Chaliy, as their de facto mayor, chanting: "A Russian mayor for a Russian town."
Many residents have long been indignant that Sevastopol was deprived of the right to elect a mayor by the political centre in Kiev, which had named the top city official since 1992.
Founded by Russia in the 18th century, the city of 350,000 was still directly under Moscow's authority until as late as 1978, almost a quarter of a century after Khrushchev's present to his native Ukraine.
"Crimea has historically never belonged to Ukraine," said Golovan, who is 48. "We want historical justice. This is an exclusively Russian city. It was and will remain so."
A sign scrawled across the road block quotes a phrase President Vladimir Putin once used to dismiss protesters in Moscow demanding his exit from politics, comparing them to chattering monkeys, termed Bandar-logs in Rudyard Kipling's Jungle Book. It reads: "Bandar-Logs shan't pass."
Putin has done little to fuel hopes of secession by Crimea, but Russia flexed its muscles by holding war games this week near the border with Ukraine.
In a sign of the tension in Crimea, at least 20 men wearing the uniform of Russia's Black Sea fleet and carrying automatic rifles surrounded a Ukrainian border guard post in the Balaclava district on Friday.
In a tense standoff, Ukrainian border police in helmets and riot gear inside the border post kept the gate shut and metal riot shields were placed behind the windows as protection.
A servicemen who identified himself as an officer of the Black Sea Fleet told Reuters jokingly: "We are here for joint military exercises, so as not to have a repeat of the Maidan," referring to the epicentre of the protest movement in Kiev.
Ukrainian officials laughed off this suggestion.
The new leadership in Kiev has accused the Kremlin of commanding the armed groups in Crimea, some of whom have taken control of the regional parliament, a military airfield and Simferopol international airport. The Kremlin denied this.
Informal militias were formed as the protests in Kiev gathered steam and Yanukovich's rule collapsed. Some are Cossacks, the men on horseback who patrolled the Russian empire's borders, and some fought for the Soviet Union in Afghanistan.
At the checkpoint barring the way to Sevastopol, most were residents of a nearby village.
The presence of Russia's fleet - whose lease was extended until 2042 by Yanukovich in exchange for cheap Russian natural gas - has long been a thorn in the side of some Ukrainians, who think it preserves too close a relationship with Ukraine's former Soviet masters.
Many of the base's 15,000 servicemen have settled in the imperial-era, whitewashed port city since retiring. Locals mostly see it as a guarantor of safety as well as an economic lifeline in the winter months when there are few tourists.
Moscow has not responded directly to calls for secession, but a number of Russian lawmakers have visited Crimea, and are given a hero's welcome.
"If the people have a right to rise up in a revolt and overthrow the authorities, why doesn't Sevastopol have a right to do that?" firebrand Russian nationalist Vladimir Zhirinovsky said to cheers in Sevastopol.
"You will always have Russian gas. You will always have millions of Russian tourists!," he said.
The crowd roared back: "Thank You!"
Not everyone among the ethnic Russians, however, favours secession or admires Putin.
"We want to be fully autonomous ... We don't need the current Ukrainian authorities, and we don't need Russia," said Galina Dudina, 60, a pensioner who has been protesting outside city hall since the weekend.
"Here people don't support Putin. Rather we think of Russians as our brothers," said Maxim Lovinetsky, 23.