BY KEVIN G. HALL
Knight Ridder News Service

MONTEVIDEO, Uruguay - Socialist Tabaré Vázquez won a majority of votes for president in Uruguay on Sunday, adding his nation to South America's political swing to the left and potentially denying the United States an important ally in the region.

Vázquez declared victory Sunday night. He spoke from the balcony of the Hotel Presidente in front of an estimated half-million people swarming the streets and said, ``Celebrate, Uruguayans, celebrate! This victory is yours!''

Vázquez then held a brief news conference announcing his transition team would begin work today, because ``we don't have any time to waste.''

No official results were released Sunday night, but the two main polling groups gave nearly identical figures of 51 percent for Vázquez of the Broad Front leftist coalition and 34 percent for runner-up Jorge Larranaga of the National Party. The exit polls did not give a margin of error.

Because Vázquez appeared to win more than 50 percent of the vote, he avoided a runoff. If it had gone to a runoff, conservatives could have united and denied him the presidency, as in 1994 and 1999.

Even before the voting had ended, tens of thousands of Uruguayans flooded the capital city of Montevideo in a sea of red, blue and white flags -- the color of Vázquez's Broad Front. The Broad Front took control of 40 percent of the congress in 1999, and was expected to build on that Sunday. The group was projected to win in the House and Senate.

''I think what we are seeing is not one more election or a changing of persons. We are seeing the beginning of a new phase in Uruguayan political life,'' said Congressman Martín Ponce de León, noting that the Broad Front has kept power wherever it won it.

The 11-party Broad Front, founded in 1971, was helped by successive economic crises in Brazil and Argentina that provoked in Uruguay a 12 percent economic plunge in 2002, and tarnished Uruguay's traditional parties as inept.

More than 30 percent of Uruguay, once considered the Switzerland of South America, now lives in poverty. Vázquez promises an emergency social program if he assumes the presidency on March 1.

About the size of Washington state with a population of 3.4 million, Uruguay holds political significance to the United States. It has been one of the Bush administration's few reliable allies in South America, where leftist or populist governments wary of Washington rule in Brazil, Argentina, Chile, Paraguay, Ecuador and Venezuela.

Uruguay's conservative departing president, Jorge Batlle, backed the U.S. push for freer trade in the Americas and U.S. attempts to isolate Cuban dictator Fidel Castro. Uruguay offered United Nations resolutions in 2002 and 2003 condemning Cuba's human rights record.

Vázquez, 64, vows to restore relations with Cuba, which Uruguay severed in April 2002 after Castro insulted Batlle as a Washington lackey. He also vows to prioritize relations with Brazil, the U.S. policy rival in South America. Uruguay's close ties to Washington, rewarded this month with an open-skies aviation agreement and a bilateral investment pact, severely strained relations with neighbors Brazil and Argentina.

In recent months, Vázquez reached out to conservative parties, global lenders and business leaders. He vowed to pay Uruguay's burdensome $12 billion foreign debt.