The three men vying to replace Margaret Thatcher as prime minister Saturday picked up key endorsements while a public opinion poll showed each of them beating the Labor Party in the next general election.

Michael Heseltine, the renegade Conservative who on Tuesday fought Thatcher to a draw in the first round, prompting her resignation Thursday, won the backing of Geoffrey Howe and Nigel Lawson, two prominent Conservatives who resigned from Thatcher's government over her European policies.The two other candidates, Douglas Hurd, the foreign secretary, and John Major, the chancellor of the exchequer, both were given commitments by other members of the Thatcher Cabinet.

The 372 Conservative members of Parliament will vote in secret Tuesday for the leader of their party, who automatically will become prime minister.

Thatcher will step down as prime minister after 111/2 years on Tuesday if one of the three contenders secures a simple majority.

If no candidate wins 187 votes, a third and final round will be held Thursday under different rules guaranteed to produce a victor.

The Conservative Party, which has been trailing in the public opinion polls with Thatcher as prime minister, would beat the Labor Party with any of the three contenders as leader, according to a Harris opinion poll.

The poll said Conservatives would have a 10 percent lead with Heseltine as leader, a 7 percent margin with Major and a 4 percent advantage with Hurd.

However, Britain's bookies, who are enjoying a boom in business, put Major as the favorite, followed by Heseltine with Hurd trailing in third.

Thatcher meanwhile was spending her last weekend as prime minister packing at her official residence at 10 Downing St. She later planned a final visit to Chequers, the prime minister's official country residence.

On Monday, the moving vans begin taking her belongings to her new home in Dulwich, outside London.