The General Accounting Office issued a sharp attack yesterday on the Reagan administration's latest proposals to beef up work requirements for welfare clients.

Joseph Delfico of the GAO's human resources division told a House subcommittee that the administration's plans are based on insufficient evidence, would drastically cut federal aid to the states while forcing them to serve more clients, and could lead the states to shift money out of expensive programs for those who are hardest to employ to spread the reduced funds farther.

But Jo Anne B. Ross, who administers the Aid to Families with Dependent Children program, countered that "exciting things are going on in welfare work programs" because of the administration's efforts to force mothers into job programs designed to keep them off the rolls. "Finally," she said, "the work ethic has become an operating principle in the welfare system."

Ross said four years after the administration began promoting work programs for welfare clients, she found that "people were not only gaining skills and finding jobs, they were also finding a new or renewed sense of pride and self-worth. And they were using their new-found confidence and abilities to take responsibility for their own lives and economic support by moving into unsubsidized jobs."

She said these findings justify moving forward with additional work requirements for welfare mothers and requiring states to develop their own programs. At present, the work requirements supported by the administration are not mandatory and are in effect in fewer than half the states.

Under the proposals, the current $267 million Work Incentive (WIN) grant program to the states would be replaced by a $145 million program that would increase to $287 million by fiscal 1989.

Welfare recipients, except those who are elderly, disabled or have very small children, would be required to conduct an organized job search, gain experience in a community job for no extra compensation beyond the welfare payment, or participate in related activities. By the third year, 75 percent of all eligible welfare recipients would have to be included in the program.

Delfico said that while some of the projects cited by Ross are promising, "rigorous evaluations are not being conducted" by the government on a large scale. "In many cases," he said, "evaluations have been done poorly, monitoring is haphazard" and "there is little evidence to date that these programs can be implemented on a large scale or that they achieve savings in public expenditures.

"Instead," he said, "a national mandatory program could increase day care, transportation and administrative costs." Moreover, he added, by cutting federal funds, the proposal might force the states to abandon the kind of expensive programs that might be most helpful for long-time welfare mothers who have real trouble finding jobs.