PHOENIX — A government report questions the effectiveness of a federal program, long criticized by immigrant advocacy groups, that deputizes police officers as immigration  agents.
The report, to be released Wednesday by the Government Accountability Office , the investigative arm of Congress, says the government has failed to determine how many of the thousands of people deported under the program were the kind of violent felons it was devised to root out.
Some law enforcement agencies had used the program to deport immigrants “who have committed minor crimes, such as carrying an open container of alcohol,” the report said, and at least four agencies referred minor traffic offenders for deportation.
Homeland Security Secretary Janet Napolitano  has already ordered a review of the program. A top official at the Immigration and Customs Enforcement  agency is set to testify at a Congressional hearing on Wednesday.
Known as 287(g), a reference to the section of a 1996 law authorizing it, the program has been promoted by immigration officials as an important tool in deporting serious criminals. It has also enjoyed the strong support of some local law enforcement agencies, including here in Maricopa County, where the sheriff operates the largest program, with 160 trained deputies.
But the report said immigration bureau officials had not closely supervised how their agreements with the local agencies had been carried out, had inconsistently described the program’s goals and had failed to spell out what data should be tracked, collected and reported.
A spokesman for the Homeland Security Department , to which the immigration agency referred calls, did not respond to telephone and e-mail messages. In a response included in the report, agency officials said they had put in place changes, many of them late last year, that address the report’s findings.
The officials said the agency supported the report’s five recommendations, including clarifying the circumstances under which 287(g) authority should be used, spelling out the agency’s supervisory role and establishing ways to measure performance. The agency said it would release details in the next two months on how it would improve the program, which received $54 million from Congress this year.
The report analyzed 29 of the 67 local law enforcement agencies in the program. It found that they arrested 43,000 illegal immigrants last year, including 34,000 taken into custody by the immigration bureau.
Of the 34,000, the report said, about 41 percent were put in removal proceedings, 44 percent waived their right to a hearing and were immediately deported, and 15 percent were released for reasons including humanitarian grounds, the “minor nature of their crime” and their having been sentenced to prison.
Citing lapses in data collection, the G.A.O. was unable to determine how many of the arrested immigrants were suspected of committing serious crimes.
The 287(g) law authorizes the immigration agency to train local and state law enforcement to use its databases to determine legal status and take the first steps in deportation proceedings, but it does not specify which kinds of illegal immigrants to focus on.
The G.A.O. report said senior managers at the agency told investigators the main goal of the program was curtailing violent crimes, human smuggling, gang activity, drug smuggling and other high-priority offenses. But the agency, the report said, had failed to document that goal clearly in its agreements with the agencies.
Representative Bennie Thompson, a Mississippi Democrat and chairman of the Homeland Security Committee, which will hold the hearing on Wednesday, said in a statement that “the record is incomplete, at best, as to whether this program is a success.”
“Without objective data, we cannot evaluate the effectiveness of this program, nor can we determine whether better results could be achieved by other means, such as increasing the number of ICE agents,” he said.
The report did not conclude whether local agencies in the program had engaged in racial profiling, a top concern Mr. Thompson has raised before and a chief complaint in Maricopa County.
Sheriff’s deputies here have arrested thousands of illegal immigrants, many of whom were stopped for traffic violations, in sweeps that have led to lawsuits accusing the department of racial profiling.
Use of the program has accelerated in recent years as the immigration debate intensified. It has grown to 67 agencies in 23 states with more than 950 deputized officers, from 5 law enforcement agencies in 2005; there is a waiting list of 42 agencies.
Representative Lamar Smith , Republican of Texas, who was instrumental in getting the program started in 1996, said, “Law enforcement officials believe that this voluntary program works.” He added, “Those who are serious about public safety should call for its expansion.”
The G.A.O.’s criticism largely mirrored the findings of recent analyses by independent groups, including a report last week by Justice Strategies, a nonpartisan research foundation in Brooklyn. It found, among other problems, that the program might actually strain local resources because people who have not committed a serious crime are being held on immigration charges.