Rivals for Thatcher Job May Go to Runoff Vote : Britain: None of the 3 candidates can claim a majority heading into today’s balloting in Parliament.

The brief, gentlemanly but hard-fought contest among the three candidates to become Britain’s new prime minister ended late Monday with the clear possibility that none would win today’s election.

If so, another ballot would be necessary on Thursday to determine who will succeed Margaret Thatcher as leader of the Conservative Party and the British government.

In a final assessment Monday, former Defense Secretary Michael Heseltine seemed to be the front-runner, with Chancellor of the Exchequer John Major close behind and Foreign Secretary Douglas Hurd trailing both.

Since the secret vote for a new Conservative Party leader--who, given the Conservatives’ majority in Parliament, will automatically become prime minister--is taken only among the 372 Tory members of Parliament, there have been no reliable polls from major sampling organizations.

Instead, the three candidates have all claimed mounting strength among their colleagues in the House of Commons, but none has claimed that he will gain the necessary 187 votes to win outright today.

And even the candidates admit that their colleagues have often in the past dissembled about who will actually get their votes.

On Monday, aides of the outgoing Thatcher revealed that Major was her favorite and the man for whom she would vote.

“She regards him as a true man of the people,” said a close adviser, adding that Major seems to be the best candidate to represent “Thatcherism.”

Major’s supporters stress that he is the true inheritor of Thatcher’s policies but at the same time offers a popular image to independent voters with his call for a “classless” society.

The three candidates have presented remarkably similar policies, and so their colleagues may vote on the basis of other considerations.

Heseltine reminded his colleagues Monday that he was running ahead of any other Tory leader in nationwide popularity contests and best suited to unite the party and lead it to victory against the opposition Labor Party in the next general elections.

The Conservatives can call a new election anytime during the next 18 months.

The three-sided campaign began Thursday, when Thatcher, crippled by Heseltine’s strong showing in the first-round voting for party leader last Tuesday, announced her intention to resign.

At the beginning of the campaign, the 57-year-old Heseltine seemed the most popular, but he has run into the backlash of fervent Thatcher supporters who blame his challenge for bringing her down. He thus must deal with the prospect of votes being cast not only for him but against him.

The 47-year-old Major, whose exchequer post is the equivalent of Treasury secretary in the United States, declared that his experience in economics suits him to lead the country through the current economic recession and that as the youngest contender, he is the man of the party’s future.

Hurd, 60, and his supporters claimed that he has held the toughest executive jobs--foreign secretary, home secretary, Northern Ireland secretary--and is therefore best qualified to lead the nation in a period that might see it fighting a war in the Middle East.

Whoever the winner, all members of the Conservative Party were bolstered by weekend public opinion polls showing all three candidates individually running stronger than the Labor Party’s Neil Kinnock--figures that have caused consternation in opposition circles.

The unexpected revival of Tory party fortunes has been widely attributed to the fact that the confrontational, often abrasive leadership of Margaret Thatcher will be replaced by a more moderate leader.