WASHINGTON — Pentagon officials unveiled new policies Thursday that will cut down on the number of service members expelled each year for being gay, and they admonished a top U.S. general for publicly opposing changes to the country’s controversial “don’t ask, don’t tell” policy.

The 1993 law banning gays and lesbians from serving openly also requires the military to expel members who admit they are gay or are proven to be in formal hearings. About 13,000 have been discharged under the law.

But changes announced Thursday by Defense Secretary Robert Gates will make it more difficult to expel gays by restricting grounds for initiating an inquiry into a service member’s sexuality, limiting evidence that can be used against them and requiring that more senior officers oversee the process.

“These changes represent an important improvement in the way the current law is put into practice, above all by providing a greater measure of common sense and common decency,” Gates said.

In announcing the new procedures, Gates took the first major step of a yearlong process. For the rest of the year, a task force will study what the military will need to do to repeal the ban and, for the first time, accommodate people of varying sexual orientations.

Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, also took the unusual step of publicly chastising a three-star general for urging troops and their families to oppose the repeal. Mullen said that remarks by Lt. Gen. Benjamin Mixon, the commander of U.S. Army forces in the Pacific who urged opposition in a letter to the editor, were “inappropriate.”

Opposition by military officers to gays serving openly in the military scuttled an attempt by former President Bill Clinton to end the ban. Mullen, who has endorsed President Barack Obama’s call to repeal the prohibition, has worked to ensure that military officers do not try to thwart the move.

Advocacy groups said the changes announced Thursday were an important step toward curbing what they see as abuses of the current law, but disagreed on its precise effects.

“We don’t want these changes to be seen as a substitute for full legislative repeal, but I don’t think the Pentagon wants that either,” said Alexander Nicholson, the executive director of Servicemembers United, an organization of gay and lesbian veterans and troops.

Discharges will continue under the law. Obama was urged by advocates for gays and lesbians to issue an executive order suspending discharges under the “don’t ask, don’t tell” law. But Gates and others cautioned against taking drastic action until the military completes its yearlong review.