British Prime Minister Margaret Thatcher, seeking to ride out the gravest political crisis she has faced in more than six years in power, today rejected opposition charges that she was personally involved in a decision to leak confidential government information.

Speaking in an emergency debate in Parliament, the prime minister conceded that her Conservative government had mishandled aspects of the protracted Westland helicopter affair, which already has led to the resignations of two senior ministers. But, despite repeated protests and interruptions from her left-wing opponents, she denied that she is guilty of any wrongdoing.

Today's debate in a tense, overflowing House of Commons had the hallmarks of a great parliamentary occasion, with Thatcher as the main protagonist. Faced by an opposition onslaught on her judgment and integrity, the prime minister succeeded in rallying Conservative members of Parliament behind her but failed to quell growing criticism of her actions and those of her closest advisers in the month-long controversy.

What began as an internal Cabinet dispute over the financial rescue of the bankrupt Westland helicopter company has escalated into a major political challenge to Thatcher, with nearly daily revelations about questionable political activity and deep divisions within her government.

Although most commentators here doubt that Thatcher's position as prime minister is in immediate danger, given the solid Conservative majority in Parliament, the consensus is that her authority has been seriously and perhaps permanently weakened. Her standing in the opinion polls has plummeted, with the Observer newspaper reporting last weekend that about 43 percent of Britons believe she should resign because of the Westland affair.

The opposition censure motion was defeated by a majority of 160 after Thatcher's main Conservative party critic, former defense minister Michael Heseltine, announced that he would vote with the government. Heseltine resigned from the Cabinet on Jan. 9 after accusing Thatcher of practicing arbitrary and authoritarian methods of government.

The main point at issue in today's three-hour debate, which opposition leaders described as a parliamentary "trial" of Thatcher, was the leaking to the press on Jan. 6 of a confidential letter from the government's chief law officer that was used to discredit Heseltine. Thatcher conceded last week that the letter was leaked on the instructions of her close political ally, former trade and industry secretary Leon Brittan, with the approval of her own private office.

Under Britain's restrictive "official secrets" legislation, which Thatcher has pledged to enforce, the unauthorized leaking of information is a criminal offense. There is also a strict Cabinet rule against publicizing the private advice of government legal officers.

Thatcher, who was repeatedly interrupted by jeers and catcalls from the opposition but cheered on by her fellow Conservatives, said that she did not learn of the Jan. 6 leak until the following day. She also insisted that she did not learn of her trade secretary's involvement in the affair until receiving the results of an official inquiry on Jan. 22.

Brittan was forced to resign last Friday in response to criticism among rank-and-file Conservative members of Parliament for his handling of the affair. His action placed Thatcher, who became Conservative leader 10 years ago, directly on the political firing line.

Opposition leaders expressed incredulity today at the prime minister's insistence that she had been kept in the dark by her senior officials. The leader of the centrist Social Democratic Party, David Owen, said he feels that if her version of events was true then the officials concerned should be dismissed.

In another damaging revelation, the government acknowledged that its chief law officer had protested the leak of a letter written by him without his knowledge. In a letter to Heseltine released today, Solicitor General Patrick Mayhew said that it was clear that the confidentiality rule had been "immediately and flagrantly violated."