WASHINGTON (AP) _ The Department of Veterans Affairs has paid benefits to more than 1,200 deceased veterans, including about 100 dead a decade or more, the General Accounting Office says. The agency pegs the potential annual loss from the erroneous payments at $5.7 million.

Auditors for the congressional investigating agency said the department could have reduced the erroneous payments by matching VA benefit payment files with death information maintained by the Social Security Administration.

The department, agreeing with the GAO's findings, said it now intends to follow that procedure.

In a letter to the GAO, Edward J. Derwinski, the secretary of veterans affairs, said he concurred with the agency's findings and was moving to obtain death information from the Social Security Administration.

''Upon verification of the death, we will take prompt action to stop any erroneous payment and to resolve any overpayment that would develop,'' Derwinski's letter said.

The GAO, in a report to the Senate Veterans Affairs Committee, said, ''We found that in April 1989 VA paid compensation or benefit payments for 1,212 veterans whom Social Security Administration records reported had died at least four months earlier.

''About 100 had been dead 10 years or more.''

The Veterans Affairs Department pays out more than $14.7 billion a year in disability compensation and pension benefits to more than 2.8 million veterans and nearly 1 million surviving spouses and other dependents.

The GAO said that while benefits should be ended when a beneficiary dies, ''if surviving relatives or other knowledgeable persons do not report death to VA in a timely manner, substantial erroneous payments can result.''

The agency said the department has relied on voluntary reporting of deaths as a basis for ending benefits.

But investigators said the Social Security Administration goes much further, receiving reports of deaths from many sources and buying death certificate information from states.

Federal agencies such as the VA are authorized to obtain this information, the GAO said.

The congressional agency said that by matching VA's benefit payment file with Social Security files containing information on 39 million deaths ''we identified 1,212 veterans who were reported dead as of December 1988.''

The GAO said it first found 1,065 veterans that Social Security data showed were dead but who were still receiving VA benefits.

''Erroneous payments to these veterans' accounts could amount to $5.1 million annually,'' it said.

The GAO said it then matched the VA payment file with a Social Security file containing about 450,000 death certificates purchased from the states.

That search added an additional 147 deceased veterans whose bank accounts were continuing to receive payments. The GAO said it estimated these erroneous payments at $638,000.

The review was conducted between August 1989 and April 1990.

The Veterans Affairs Department, acting at the GAO's request, investigated several of the cases, with these results:

-A veteran, identified by Social Security as having died in August 1984, continued to receive VA benefits. Records showed that a total of $30,369 in direct deposits had been made to the veteran's bank accounts. The VA ended benefit payments, concluded that overpayments of $30,000 had been made and opened an investigation.

-Social Security records showed another veteran had died in September 1983 but the department continued to make direct deposit payments totaling $13,797. The payments were ended and the department is considering further action.

-Social Security records showed another veteran had died on Aug. 8, 1986. VA payments had been sent since then to the veteran's last known address. The VA ended payments after determining that the veteran was indeed dead and that a sister had been cashing his checks. Erroneous payments were estimated at $2,755.