A bipartisan group of U.S. senators introduced a bill on Tuesday to allow U.S. citizens to travel freely to Cuba and predicted Congress would approve it as a step toward ending the five-decade-old U.S. embargo.

"I think there's sufficient votes in both the House (of Representatives) and the Senate to finally get it passed," Democratic Senator Byron Dorgan said at a news conference.

Dorgan, whose home state of North Dakota could benefit from increased agricultural sales to Cuba, introduced the bill along with fellow Democratic Senator Christopher Dodd and Republican Senators Richard Lugar and Mike Enzi. Seventeen other senators also are sponsoring the measure. A companion bill introduced in the House earlier this year has 121 co-sponsors.

Congressional opponents of any move to ease the embargo promised a tough fight to keep this measure from becoming law.

"This is the time to support pro-democracy activists in Cuba, not provide the Castro regime with a resource windfall," Senator Mel Martinez, a Florida Republican who was the first Cuban-American elected to the Senate, said in a statement.

President Barack Obama said during last year's presidential campaign he favored easing U.S. restrictions on family travel to Cuba and the sending of cash to family members.

But he stopped short of supporting the lifting of the trade embargo, which a growing number of U.S. lawmakers believe has failed to bring about democratic change in communist-led Cuba.

Vice President Joe Biden told reporters "no" when asked in Chile on Saturday whether the United States would lift the embargo, as many in Latin American favor. 

Obama is expected to face pressure from regional leaders to improve U.S. relations with Cuba when he travels to Trinidad in mid-April for the Summit of the Americas meeting.

Washington slapped economic sanctions on Cuba in 1960 after Fidel Castro's leftist government nationalized U.S. sugar mills, oil refineries and other assets. A full U.S. embargo was enforced in 1962 as Cuba became a close Soviet ally.

Travel to Cuba by U.S. citizens was banned after the Cuban missile crisis, which brought the world close to nuclear war.

Efforts to loosen the embargo remain politically difficult because of the influence of Cuban-American emigres in Florida, a state often important in deciding U.S. elections. Staunch anti-Castro exiles argue that allowing tourism and more trade with Cuba will help prop up communism on the island.

Dodd told reporters there were not enough votes in Congress to end the embargo completely. "My sense at this point is that's a step too far," Dodd said.

U.S. farm and business groups promised to lobby hard for removal of the travel restrictions.

"The U.S. embargo on Cuba is a 50-year failure, and lifting the ban on travel is a good first step toward a more rational policy," said Myron Brilliant, a senior vice president at the U.S. Chamber of Commerce.

The United States sold $710 million worth of soybeans, wheat, poultry and other agricultural goods to Cuba last year under a law passed in 2000 that allowed food sales as long as they were paid in cash in advance. 

The Bush administration interpreted that law narrowly to frustrate sales and so far the Obama administration has said it would follow the same policy, despite recent legislation passed by Congress to overturn it.