LONDON, NOV. 23 -- John Major, a rising star as Britain's chancellor of the exchequer, and old-guard Foreign Secretary Douglas Hurd today launched their campaigns to replace Prime Minister Margaret Thatcher, but after the drama of her resignation Thursday, Britain's ruling Conservative Party appeared to be entering a calmer, less ideological era.

Major and Hurd sought to differentiate themselves from each other and from the apparent front-runner, Michael Heseltine, the Tory maverick whose political challenge triggered Thatcher's downfall after 11 years in office.

Major, who at 47 is the youngest of the three, appeared to jump ahead of Hurd in the race to catch Heseltine, portraying himself as the candidate of the future and promising to steer Britain toward "a genuinely classless society." He seemed to be inheriting the votes of many Thatcher loyalists and claimed to have the support of one-third of the party's 372-member House of Commons caucus.

By contrast, Foreign Secretary Hurd, at 60 the oldest of the three, emphasized his diplomatic experience especially in dealing with the crisis in the Persian Gulf. "The crisis is entering a crucial, critical phase," he told reporters, "and it will require cool and authoritative handling."

While the two new contenders, both of whom announced their candidacies minutes after Thatcher withdrew from the contest Thursday morning, scrambled to organize their campaigns, Heseltine acted the cool, collected front-runner, offering a few low-key press interviews but otherwise keeping a low profile.

He maintained the same theme he had adopted when he challenged Thatcher, saying that polls showed he was best placed to close the party's wide gap with the opposition Labor Party and lead Conservatives to a fourth consecutive electoral victory. A new election must be called by mid-1992.

"You may think it's hypothetical," Heseltine told one interviewer about his lead in the polls. "But to the lads and the lasses out in those marginal {parliamentary seats}, it's not hypothetical. They want to win and they believe I can win for them."

But two new polls tonight indicated that a party led by any of the three candidates would close the gap with Labor.

All three candidates sounded tones of reconciliation and party unity and promised to adopt styles of government far less confrontational and abrasive than that of their predecessor.

"I think that democratic government consists of listening, deciding, persuading," said Hurd. "You listen to views, you take a decision, in our case collectively in cabinet, and then you persuade."

Some Tory lawmakers expressed a wistful sense of loss for Thatcher's hard-edged approach but conceded the government could not and would not be the same.

"Mrs. Thatcher was so unique and such a change that she combined her own personality and her own political philosophy in a way that just won't be repeated," said David Fallon, one of the few right-wing Thatcherites to declare for Hurd.

"I don't think you're going to see Majorism or Hurdism or Heseltineism in the same way you saw Thatcherism in the 1980s," Fallon said.

Analysts said the party seemed to be quickly reverting to the pre-Thatcher era.

"Until the late '70s, the Tory party used to campaign specifically on the notion that it was the pragmatic party," said David Robertson, political scientist at St. Hugh's College at Oxford University. "Other people had isms. Other people were ideologues."

Despite the fact that they serve in her cabinet, both Major and Hurd were quick to declare that they would seek an immediate and thorough review of Thatcher's unpopular new poll tax, which funds local governments.

But both seemed vulnerable to the charge that they had not stood up against the tax when Thatcher rammed it through her cabinet two years ago.

Major sounded the most cautious note, but admitted the government had hastily adopted the poll tax, known formally as the "community charge."

"One of the major problems with the community charge was that we got bounced into decisions before they were fully thought through," he told a radio interview.

Because Heseltine stormed out of Thatcher's cabinet in 1986, before the poll tax was adopted, he is the only contender who can claim he is free from the taint of unpopularity attached to the measure. But he has other political problems in the new contest.

In the first round against Thatcher last Tuesday, Heseltine won 152 votes, enough to prevent her from winning the necessary margin she needed to avoid a second round of voting and consequently driving her out of the race.

But many of those votes came from lawmakers disenchanted with Thatcher and hoping to bring in a third candidate. Some of them are now likely to defect to Major or Hurd.

To reach the 187 votes required for victory in the next round, Heseltine needs to attract new support and he has been making appeals to Thatcherites now left without a standard bearer. Last night he appeared before the No Turning Back group, a band of right-wing legislators, and told them that his own political philosophy, which he termed "no holding back," was similar to Thatcher's.

In personal style if not ideology, Heseltine is the most Thatcher-like of the candidates. But many loyalists say they will never support him after he took the lead role in forcing Thatcher's resignation.

"The people who will unite the party are those who supported the prime minister until she stepped down, not those who wounded her," said Ann Widdicombe, a Thatcherite lawmaker.

Heseltine's campaign managers claimed they had 40 new pledges of support by this afternoon. But it is generally believed that Heseltine needs to wrap up the contest in the next round or face defeat in a third ballot next Thursday.

In that final round, voters will list a second choice, and the votes of the third-place candidate automatically will be transferred to that choice. Because Hurd and Major are cabinet colleagues, most analysts expect that supporters of each are likely to name the other as their second choice and propel one of them to victory over Heseltine in the third round.

But the other candidates must overcome perceived liabilities.

Major, who left high school at 16 and once collected unemployment benefits, has the advantage of working class origins. But he has been a cabinet member for less than four years and has little foreign policy experience. His wife, Norma, has expressed chagrin that Major has seldom had time for his family since he became chancellor last year.

Hurd is a white-haired patrician from the party's old establishment wing, which is held in little esteem by iconoclastic Thatcherites.

While the three rivals struggled to succeed her, aides said Thatcher spent a quiet day at Downing Street, where she started packing her personal belongings and mementos.

She also received a phone call from California from former president Reagan, one of her closest allies during her tenure in office.

Thatcher is not expected to endorse any candidate publicly, but many supporters say she will vote for Major, her former protege.