VICENZA (AFP) -- Tens of thousands of people were spilling out of buses and trains arriving in the northeastern city of Vicenza early Saturday to take part in a major protest against the planned expansion of a U.S. military base here, a divisive issue for Italy's center-left government.

"We were 10 to a compartment," said Gino Del Ferraro, a 23-year-old physics student who arrived on a train chartered by the Refoundation Communist party, a component of Prime Minister Romano Prodi's coalition that is fiercely opposed to the base plan along with a smaller communist party and the Greens.

Ferraro paid 10 euros (12.50 dollars) for a round trip overnight train ride from Rome.

The U.S. 173rd Airborne Brigade is currently spread across two sites in Germany and Camp Ederle, on the east side of Vicenza, and Washington wants to consolidate the Brigade here.

The U.S. embassy has put out a travel advisory urging U.S. nationals to stay away from Vicenza on Friday and Saturday, predicting a turnout of some 70,000.

The Italian press on Saturday predicted a turnout of up to 80,000, with authorities warning of violence fomented by "extremists," while organizers scoff at the idea. "The mass media are calling us extremists," boomed Oscar Mancini at a pre-march rally late Friday. "They haven't understood anything about Vicenza." Prodi on Saturday urged a peaceful protest, saying: "Demonstrations are the salt of democracy, but they should be peaceful, serene and without violence."

Vicenza's former mayor Achille Variati said the protests were also misconstrued as anti-American. "It's about us against the city administration," he told AFP.

Under the plan, the 2,750-strong Brigade will consolidate in Italy by taking in a former military airfield at Dal Molin, on the opposite side of Vicenza from Camp Ederle, at a cost of some 500 million dollars.

The plan would more than double the U.S. military footprint in Vicenza, Variati noted.

Local and regional authorities are in favor of the plan, but it is fiercely opposed by pacifists, environmentalists and residents, despite the some 1,200 local jobs provided by the base, one of seven U.S. bases in Italy.

U.S. Ambassador to Rome Ronald Spogli was hounded by protesters during a visit to Vicenza, which is some 40 kilometers (25 miles) west of Venice.

The base issue is one of several that are troubling bilateral relations since Prodi came to power in May and withdrew Italy's troops from Iraq in December. =