WASHINGTON — The Social Security Administration is not doing enough to catch the middlemen who are defrauding a federal disability program by coaching immigrants to feign mental illness and providing false medical histories, say congressional investigators and a senator.

According to the General Accounting Office, scams by middlemen, who help non-English-speaking immigrants obtain disability benefits from Supplemental Security Income, are draining millions of dollars from the government’s largest cash welfare program for the poor.

The findings by the GAO, the congressional watchdog agency, were released Sunday by Republican Sen. William Cohen, chairman of the Senate Special Committee on Aging.

Cohen, whose oversight of the SSI program also exposed widespread abuses by drug addicts and alcoholics who collect cash disability, said the explosion in the number of immigrants applying for SSI has created an atmosphere ripe for fraud.

“Translators have become wise to how easy it is to defraud the system and are actively seeking out immigrants as clients,” Cohen said.

Yet Social Security, which oversees the $22 billion-a-year SSI program, “is simply not doing enough to weed out these crooks, and it is costing the taxpayers millions of dollars every year,” Cohen said.

The GAO reached a similar conclusion, saying that while Social Security is planning several initiatives to detect middleman fraud, “more could be done.”

In her response to the GAO’s findings, Social Security Commissioner Shirley Chater said the agency is working to identify SSI recipients who got on the rolls through fraudulent means.

Social Security is also hiring more bilingual staff, and its ultimate goal “is to dramatically reduce reliance on middlemen in developing claims of non-English-speaking applicants,” Chater said.

The number of legal immigrants collecting SSI disability has increased sixfold over the past decade, from 45,000 in 1983 to 267,000 in 1993. By comparison, the number of U.S. citizens on the rolls grew less than twofold, from 2.3 million to 4.2 million.

To be considered eligible for SSI disability benefits, a person must be poor and unable to work because of a physical or mental impairment expected to last at least 12 months or result in death.

Non-English-speaking applicants for SSI are allowed to provide their own interpreters for interviews with the agency about their claims for benefits if Social Security does not have a translator available, the GAO said.

According to the GAO, some of the immigrants’ translators have coached them to claim forms of mental impairment, such as delayed stress syndrome or depression.

The middlemen have also controlled interviews with Social Security by answering all questions, preparing applications for numerous people using identical wording to describe the same mental impairments, and establishing relationships with unscrupulous doctors who help them defraud SSI by submitting false medical evidence, the GAO said.

The middlemen are then paid a fee; in one case the middleman received between $2,000 and $3,000 per applicant.