House Ways and Means Committee Chairman Al Ullman (D-Ore.) yesterday unveiled a welfare revision proposal estimated to cost $12 billion a year less, to provide few public-service jobs and furnish less fiscal relief to the states than President Carter's welfare plan.

Ullman said he intends to offer his plan as a substitute for the Carter proposal some time during subcommittee and committee action on welfare revision.

A special House subcommittee headed by Rep. James C. Corman (D-Calif.) resumes work today on the Carter plan. Corman opposes the Ullman substitute but has said he expects the issue to be decided in a head-to-head clash on the House floor.

Ullman's theory is that his less costly, more modest plan has a better chance of passage than does Carter's.

Both plans provide for a basic $4,200 minimum national welfare benefit for a family of four (consisting of a parent and three children) without other sources of income. However, the Ullman plan, far less broad in scope, differs markedly in a number of respects and would alter the welfare system less radically. Here are some of the major differences:

Childless couples and single persons wouldn't be eligible for federal cash welfare benefits under the Ullman plan unless they are aged, blind or disabled. The Carter plan, as approved so far by the Corman subcommittee, makes low-income couples and single persons eligible for federal cash aid even if they are young, childless and able-bodied, as long as they can't get work at adequate pay.

The Ullman plan would continue the food stamp program for families with dependent children, and part of the $4,200 a year benefit (about $1,650 of it) would be in the form of food stamps. For aged, blind and disabled persons it would wipe out food stamps and raise cash benefits $15 a month per person to compensate. Carter's plan abolishes food stamps and would give welfare recipients cash in their place; the entire $4,200 would thus be cash.

The Ullman plan would provide a higher earned-income tax payment rate (a Treasury payment of $1,000 to supplement earnings of a person making $5,000, for example) than would the Carter plan, thus rewarding work by a welfare recipient or low-income earner more highly.

The Ullman plan would provide, in effect, lower federal reimbursement to states that have welfare benefit levels above federal minimums.

The Ullman plan would provide 500,000 welfare public service jobs for able-bodied workers in two-parent families who can't find work. The Carter plan would provide over 1 million. The Ullman plan would tax unemployment insurance benefits for the first time.

Ullman aides calculated that the Ullman plan would cost the federal government about $8 billion a year more in 1982, the first full year in effect, than current welfare programs.