Thousands of homeless people entitled to veterans' benefits or federal welfare payments for the aged, blind and disabled are not getting them, according to Rep. Ted Weiss (D-N.Y.), chairman of a House subcommittee that has crisscrossed the country the past three months.

Weiss, in Dec. 27 letters to Veterans Administration chief Harry N. Walters and Health and Human Services Secretary Margaret M. Heckler, said his subcommittee "has found homelessness to be a national problem of epidemic proportions." Estimates range from several hundred thousand to 3 million.

Weiss said the subcommittee has heard testimony that "many of the homeless are eligible for benefits from the Social Security Administration, such as Supplemental Security Income" for the needy aged, blind and disabled, or "for VA benefits and health care," but are not getting benefits because of special problems in providing aid to the homeless. In many cases, homeless people are not aware of their eligibility, or for a variety of reasons, such as fear or mental illness, do not heed invitations to apply.

Weiss did not estimate in the letters how many eligible homeless were not receiving benefits. But an aide said Weiss, on the basis of hearings and interviews, believes that the number totals many thousands, perhaps hundreds of thousands.

A VA spokesman said the agency did not know how many homeless people are entitled to veterans' benefits, and no estimates were available from HHS on how many homeless might qualify for SSI.

In his letters to Walters and Heckler, Weiss asked them to find those among the homeless who are entitled to benefits and take steps to see that they get them.

He wrote Heckler, "I know that you share my concern about homelessness, as evidenced by the creation of the Federal Task Force for the Homeless within HHS . . . . However, the subcommittee's review indicates that the Task Force has been ineffective, primarily because of the lack of cooperation from other federal agencies and the insufficient resources provided by HHS."

The VA spokesman said that the VA already is engaged in outreach to such people through the Federal Task Force for the Homeless.

The Health and Human Services Department for a number of years has had a program to reach people who are potentially eligible for SSI. A spokesman said there has been a special nationwide effort during the past year, asking directors of soup kitchens and shelters to encourage the homeless to apply, and working with mayoral offices around the country.

A Heckler spokesman said she shares Weiss' concern for the homeless but does not believe that the task force has been ineffective. A major problem, the spokesman said, has been actions by states and localities to remove people from mental health and other institutions without providing supervision afterward.