HONG KONG, July 16 — The combative secretary of security here, who led a push for stringent internal-security laws that prompted 500,000 people to march in protest on July 1, announced tonight that she had resigned, in what appeared to be another big victory for this city's democracy movement.

Regina Ip has overseen the city's police, immigration, customs and other uniformed officers since July of 1998, and has often been seen as Beijing's enforcer here. She kept a sword from the People's Liberation Army at the front of her desk and consistently took the lead on controversial issues, such as ordering immigration officers to raid homes last year to find people who had lost the right to live in Hong Kong after Beijing intervened in a legal battle here.

The proposed security legislation, demanded by Beijing but deeply unpopular here, proved the touchiest issue of all for Mrs. Ip. As other Hong Kong officials hung back, including Tung Chee-hwa, the territory's chief executive, Mrs. Ip took the lead in trying to persuade the public and the Legislature to accept the bill.

Her efforts became almost as controversial as the bill itself, and demonstrators toted effigies of her at the July 1 march and more recent rallies. Three days before the march on July 1, she declared that she would not feel any pressure no matter how many people showed up, and suggested that people might go only because they had nothing better to do on the holiday, the sixth anniversary of Britain's handover of Hong Kong to China.

Mrs. Ip and Mr. Tung said in separate statements this evening that she had actually submitted her resignation on June 25, and that Mr. Tung had tried to talk her out of it before finally accepting it. Under the employment contracts for top officials here, resignations become effective 30 days after submission if they are accepted, so Mrs. Ip will leave office on July 25.

The government's insistence that Mrs. Ip gave her resignation three weeks ago, but that nobody found out about it until now despite massive local and international media coverage, struck political experts as significant. "The government obviously doesn't want it to look like she's resigning under pressure from the demonstrations," said Michael Davis, a professor of law and public affairs at the Chinese University of Hong Kong.

Mr. Tung did not announce a successor for Mrs. Ip. As a minister-level appointment, her successor must be approved first by Beijing. Filling the job could be difficult, as talented people with political futures may be leery of a position that frequently involves choosing between what Beijing wants and what local residents want.

In an open letter addressed to "citizens of Hong Kong," Mrs. Ip said without elaborating that her decision was "entirely due to personal reasons." Mrs. Ip had taken a short personal leave at the end of December because of what a government official described at the time as stress related to the controversy over the security legislation.

In her letter, Mrs. Ip strongly defended the security bill, which would set long jail sentences for sedition, subversion, secession and treason. She said that she deeply regretted that the legislature has not yet passed the bill and added that, "I am confident that my successor will be able to accomplish this task in good time."

Mr. Tung announced on July 5 that he was removing three of the most controversial provisions from the bill, including one that would have allowed Mrs. Ip, as secretary for security, to ban any Hong Kong group that was subordinate to an organization banned on the mainland for national security reasons.

But the march so rattled the city's business leaders that the chairman of the pro-business party resigned from Mr. Tung's cabinet the following night. That left Mr. Tung without the votes to push the bill through the legislature and forcing him the next morning, July 7, to postpone further consideration of the bill.

No new timetable has been set for the bill, which Mr. Tung and Mrs. Ip had wanted the Legislative Council to pass on July 9.

The July 1 march was the largest public demonstration in the People's Republic of China since the Tiananmen Square protests that the Chinese military bloodily suppressed in 1989. After giving unclear and even contradictory signals in the first week after the rally here, Beijing has been taking a harder line lately.

Gao Siren, the head of Beijing's liaison office here, called on Tuesday for Hong Kong residents to focus more on the economy than on politics.

Mr. Tung's decision to accept Mrs. Ip's resignation is striking not just because it inevitably gives the appearance that Beijing is yielding to public pressure, but also because of Mr. Tung's refusal over the past year to accept the resignations of other senior officials. Antony Leung, Hong Kong's financial secretary, offered his resignation this spring after it emerged that he bought a luxury car six weeks before announcing the government would more than double the taxes on such cars.