NEWS ANALYSIS : Thatcher’s Woes Boost Speculation: Will She ‘Crack’ Under the Heat? : Britain: The prime minister’s future is clouded by a drop in popularity. She says she’s not ready to retire.

A subtle but significant change has crept into the seemingly incessant speculation here about Prime Minister Margaret Thatcher’s political future.

While the focus has previously been on such outward signs of her problems as plummeting popularity ratings and humiliating anti-government demonstrations, it now seems increasingly to deal with her state of mind.

A senior Parliament member from Thatcher’s own Conservative Party volunteered at the end of an interview the other day that he thinks the British government can still turn its fortunes around “if she keeps her nerve.”

Speaking between hors d’oeuvres at a cocktail party, an admiring Western diplomat said the main, near-term question about the prime minister is whether she will “crack.”

And even one of her aides conceded that a much discussed scenario has her so overcome by depression at the state of her administration that she resigns.

The aide quickly dismissed that possibility. “We’re not for mid-term cracking!” he assured.

In fact, few claim to see any obvious signs that Thatcher is buckling under the political pressure. And she makes light of such suggestions.

“I did not come here to retire,” she assured party stalwarts with a smile in the opening lines of an address shortly after her party suffered a stunning defeat in a parliamentary by-election.

In a luncheon speech to the Scottish Distillers’ Assn. not long before, she said: “As I come up to the 11th anniversary as prime minister (May 4), I take great comfort from the fact that malt whiskies reach their full maturity only in the 12th year--and after that, there is a premium in their price and their value.”

Still, the fact that even one of her closest Tory collaborators would call into question her nerve is a remarkable change in the image of the woman Moscow once dubbed the “Iron Lady.” Skeptics may have doubted whether Thatcher was skilled enough to control the fire, but until now they seldom suggested that she couldn’t stand the heat.

The change occurs on the eve of a summit meeting with President Bush in Bermuda today that should theoretically provide a welcome reprieve. Leaders the world over count on high-visibility foreign forays to deflect attention from domestic problems.

This visit, however, seems to be generating more British press comment about Thatcher’s allegedly diminished role on the world stage. It hasn’t diverted attention from her troubles at home; it threatens to compound them.

“In the 14 months since Mr. Bush’s inauguration, the balance of Atlantic and European power has shifted quite dramatically,” wrote Peter Jenkins, a widely read political columnist for The Independent newspaper. “The Soviet Union has become a less formidable adversary; Germany--about to be united--the dominant Western European power, while Britain has looked increasingly isolated from the mainstream of international developments. This has diminished Mrs. Thatcher’s usefulness to Washington.”

The press here has also picked up the psychological theme.

The relatively pro-Thatcher Sunday Times editorialized the other day that she “is clearly entering a night of the soul.” The Independent ran a lengthy piece of commentary on “what makes prime ministers give up the ghost.”

Several papers have probed the possible psychological implications of new, 10-foot high gates that now block the end of Downing Street, where No. 10 is Thatcher’s official residence. One psychiatrist was quoted as saying that the person so protected must feel “an enormous sense of isolation and betrayal at the hands of people who had failed to be grateful for years of selfless public service.”

Probably more pertinent is that a Thatcher abdication seems the only likely way this government will change before the next general election, scheduled for mid-1992. With a 98-seat majority in Parliament, her Tory party doesn’t have to worry about votes of confidence in the meantime.

Theoretically, she could face a leadership challenge from within her party that, if successful, would also force her out of No. 10. A Sunday Times poll of 100 Conservative members of Parliament last month found one in four saying that Thatcher should stand down before the next election.

But there is no clear-cut successor, and a possibly bitter struggle to replace her could damage the party badly. Former Defense Minister Michael Heseltine appears to be the front-runner in any succession race, but former party chairman and spokesman of the party’s right wing, Norman Tebbit, has pledged to fight rather than see Heseltine take over.

“The scenario I think is quite likely is that when she becomes convinced that she’ll lose the next election, she’ll go quietly,” commented author and political scientist Anthony Sampson.

Thatcher is now the most unpopular prime minister since Gallup began polling here 50 years ago, with only one in four Britons approving of the job she is doing. All the polls show the Conservatives trailing the arch-rival Labor Party by at least 20 points, with the gap widening.

Sampson speculated that Thatcher may step down voluntarily before next fall’s annual Conservative Party convention. She could “go in a respectable way by using Denis (her husband) as a pretext,” he added. Denis Thatcher is 10 years older than the prime minister, who will be 65 in October.

Thatcher insists she intends to run for a fourth term. And her strategists present a cogent case that she could still pull it off.

They concede that the economy, an issue that has helped her tremendously in past elections, has turned sour, with interest rates at a punishing 15% and the latest inflation figures, released Thursday, showing prices headed upward at more than an 8% annual rate. However, her strategists see a turnaround by the end of the year.

By then they hope that a combination of time and tinkering will have made the highly unpopular “poll tax” for local government services more acceptable.

Even under that scenario, however, a harsh test of the “Iron Lady’s” mettle is likely over the next several months.

The Conservatives face a drubbing in local elections scheduled for May 3. The initial installment payments are due on the new “poll tax” later this month, and soon opponents of the levy promise that a boycott campaign will force the government either to back off or start throwing ordinary people into jail. Neither option would do much for Thatcher’s popularity.

As The Economist weekly put it the other day: “The idea that Mrs. Margaret Thatcher may no longer be prime minister by the autumn must now be taken seriously.”