Most of the listed complaints were summarized only in general terms such as “allegation of abuse,” making them hard to evaluate. A few may have been complaints about the same incident. But trends emerged from the details. For example, there were at least 60 complaints in which detainees or witnesses accused agents or supervisors of kicking or stomping on detainees, often after they were handcuffed or on the ground, including one who said an agent had broken his nose.

At least 45 complainants alleged that agents had hit them with objects, often in the head or face. A child who crossed the border near Tucson in 2011 said an agent “hit him on the head with a metal flashlight 20 times, kicked him five times, pushed him down a hill.”

There were six accusations of sexual abuse and 14 of improper searches or touching. One woman said a Border Patrol agent had fondled her, breathed heavily and called her “baby.” (The records showed no action was taken.)

Lawyers with the American Immigration Council argue that these examples showed that Customs and Border Protection and the Department of Homeland Security have failed to adequately train or discipline agents as their ranks have grown significantly to more than 21,000.

Federal officials have generally rejected that assertion, but several other studies have also shown that complaints have been routinely ignored as Customs and Border Protection has expanded.

An independent assessment of the agency’s most violent cases by the Police Executive Research Forum, a group of law enforcement experts, recently criticized its “lack of diligence” in investigating agents who fired their weapons. The agency has since tightened its use-of-force policy, limiting when weapons can be fired. But many immigrant advocates said the complaint system needed to be fixed immediately.

Two members of the House from border states — Representative Beto O’Rourke, a Texas Democrat, and Representative Steve Pearce, a Republican from New Mexico — have introduced legislation that would create a new complaint system, independent of the agency, and a border oversight commission with the authority to issue subpoenas.

“C.B.P. has grown so quickly in the last 10 years,” Mr. O’Rourke said. “Many of the processes and safeguards that you would typically have in an agency of this size are simply missing.”