Under the current surveillance guidelines, the F.B.I. cannot send undercover agents to investigate groups that gather at places like mosques or churches unless investigators first find probable cause, or evidence leading them to believe that someone in the group may have broken the law. Full investigations of this sort cannot take place without the attorney general's consent. Since Sept. 11, investigators have said, Islamic militants have sometimes met at mosques - apparently knowing that the religious institutions are usually off limits to F.B.I. surveillance squads. Some officials are now saying they need broader authority to conduct surveillance of potential terrorists, no matter where they are.

The attorney general's surveillance guidelines were imposed on the F.B.I. in the 1970's after the death of J. Edgar Hoover and the disclosures that the F.B.I. had run a widespread domestic surveillance program, called Cointelpro, to monitor antiwar militants, the Ku Klux Klan, the Black Panthers and the Rev. Dr. Martin Luther King Jr., among others, while Mr. Hoover was director. Since then, the guidelines have defined the F.B.I.'s operational conduct in investigations of domestic and overseas groups that operate in the United States.

Some officials who oppose the change said the rules had largely kept the F.B.I. out of politically motivated investigations, protecting the bureau from embarrassment and lawsuits. But others, including senior Justice Department officials, said the rules were outmoded and geared to obsolete investigative methods and had at times hobbled F.B.I. counterterrorism efforts.

Mr. Ashcroft and the F.B.I. director, Robert S. Mueller III, favor the change, the officials said. Most of the opposition comes from career officials at the F.B.I. and the Justice Department. A Justice Department spokeswoman said today that no final decision had been reached on the revised guidelines.

The relaxation of the guidelines would follow administration measures to establish military tribunals to try foreigners accused of terrorism; to seek out and question 5,000 immigrants, most of them Muslims, who have entered the United States since January 2000; and to arrest more than 1,200
people, nearly all of whom are unconnected to the terrorist attacks of Sept. 11, and hold hundreds of them in jail.

Senior career F.B.I. officials complained that they had not been consulted about the proposed change - a criticism they have expressed about other Bush administration counterterrorism measures. When the Justice Department decided to use military tribunals to try accused terrorists,
and to interview thousands of Muslim men in the United States, the officials said they were not consulted. Justice Department officials noted that Mr. Mueller had endorsed the administration's proposals, adding that the complaints were largely from older F.B.I. officials who were resistant to change and unwilling to take the aggressive steps needed to root out terror in the United States. Other officials said the Justice Department had consulted with F.B.I. lawyers and some operational managers about the change.

Several senior officials are leaving the F.B.I., including Thomas J. Pickard, the deputy director. He was the senior official in charge of the investigation of the attacks and was among top F.B.I. officials who were opposed to another decision of the Bush administration, the public announcements of Oct. 12 and Oct. 29 that placed the country on the highest state of alert in response to vague but credible threats of a possible second terrorist attack. Mr. Pickard is said to have been opposed to publicizing threats that were too vague to provide any precautionary
advice.

Many F.B.I. officials regard the administration's plan to establish military tribunals as an extreme step that diminishes the F.B.I.'s role because it creates a separate prosecutorial system run by the military.

Few were involved in deliberations that led to the directive Mr. Ashcroft issued this month to interview immigrant men living legally in the United States. F.B.I. officials have complained that the interview plan was begun before its ramifications were fully understood.

The arrests and detentions of more than 1,200 people since Sept. 11 have also aroused concerns at the F.B.I. Officials noted that the investigations had found no conspirators in the United States who aided the hijackers in the Sept. 11 attacks and only a handful of people who were considered Al Qaeda members. Some at the F.B.I. have been openly skeptical about claims that some of the 1,200 people arrested were Al Qaeda members and that the strategy of making widespread arrests had disrupted or thwarted planned attacks.