Ex-Thatcher Ally to Bid for Party Leadership : Britain: Former defense secretary is expected to pose the most serious challenge since she took reins in 1975.

Former Defense Secretary Michael Heseltine will run against British Prime Minister Margaret Thatcher for the leadership of the Conservative Party, in what is expected to be the most serious challenge to Thatcher since she took over the party in 1975, close colleagues reported Tuesday.

Heseltine, a member of Parliament and a firm Europeanist, is expected to announce his candidacy today, according to widespread reports in London political circles.

Thatcher’s popularity has been at a near-low recently because of aspects of her domestic and European policies as well as her authoritarian rule in a nation used to a more collegial government.

Heseltine’s candidacy is expected to be bitterly opposed by the prime minister and leading members of her Cabinet, because of the dangers such a hard-fought contest will pose to the party in the next national election.

But his position was thought to have been bolstered Tuesday by Geoffrey Howe, former deputy prime minister, who before a packed House of Commons explained his reasons for his surprise resignation 11 days ago.

In what observers called a scathing and devastating indictment, the normally placid Howe said the prime minister was “risking the future” of the country by her negative attitude toward the European Community.

Howe, the last minister left from Thatcher’s original Cabinet, explained that his position in calling for Britain to play a leading role in the community was constantly undermined by the prime minister’s anti-European remarks.

He contrasted the positive, pro-European approach of former Tory Prime Ministers Winston Churchill and Harold Macmillan against what he called the negative “background noise” and “nightmare image” coming from Thatcher.

Howe said her view of Europe was that it was “positively teeming with ill-intended people scheming to extinguish democracy.”

“What kind of vision is that?” he asked.

Howe’s remarks were the more effective for the understated, almost diffident way he stated his case, referring to her as “my right honorable friend.”

Some embittered pro-Thatcher Tories called Howe’s unexpectedly damning speech an “incitement to mutiny” and an “act of treachery.”

On Monday night, Thatcher had appeared highly confident of any possible party contest and used phrases from cricket that vowed to knock any challenger out of the ballpark.

Referring to that analogy, Howe on Tuesday declared that the Conservatives were like a team that found their “bats broken by the team captain before the game.”

Under Tory party rules, Conservative members of the Commons will vote probably within a week on a leader in a secret ballot.

If Heseltine wins a majority--159 votes--he would become party leader, and Thatcher would be forced to step down as prime minister, though there is no set time limit to remain in the post.

The crisis in the Conservative Party began at the Rome summit of the European Community late last month when Thatcher was outvoted 11 to 1 on setting a timetable for the second phase of European monetary union in agreeing to establish a central bank by 1994.

She described the Rome proceedings as “cloud-cuckooland,” and when she spoke in the House of Commons the following Tuesday, the prime minister was equally blunt in her assessment of her EC colleagues.

That was too much for Howe, who as foreign secretary had worked strenuously to make Britain a cooperating member of the EC--before Thatcher summarily fired him from the job last year.

He turned in his surprise resignation on Nov. 2, which generated speculation about a challenge to the Thatcher leadership. That turned the focus to Heseltine, 57, who had stalked out of the Cabinet in January, 1986, in a complex dispute over the sale of a British helicopter company.

Heseltine’s lieutenants in the House of Commons say they have at least 100 sure votes for him, which would not win the leadership--but would not be a humiliating defeat.