A House subcommittee voted yesterday to slash the basic family benefit for future Social Security disability pensioners by about 15 percent below current levels.

The cut is strongly backed by the Carter administration to save money and to reduce incentives for workers to go on disability and stay there.

President Carter, in his budget message, asked Congess for $600 million in Social Security cuts, including the disability revisions. However, the disability cuts approved yesterday appear to be the only ones Congress will approve this year.

The reduction would apply only to persons going on the disability rolls after next Jan. 1. Anyone already on the rolls before then would continue to get the higher family rates. As of September 1978, 2.9 million workers and 1.9 million dependent wives, hushands and children were receiving benefits.

The Congressional Budget Office estimated that under the bill, the average male wage-earner with dependents going on the disability rolls in 1980 would get a total annual family benefit of about $7,760. Under existing law, the CBO estimated, the same man would get about $9,070.

The bill also provides various inducements to encourage disabled persons to try to return to work. These would apply to everyone on the rolls and would be effective upon enactment of the bill.

Social Security actuaries estimated that, taking all provisions into account, the bill would save the Social Socurity system about $60 million in fiscal 1980, but this would rise to $1.2 billion a year by 1984 as more and more new beneficiaries came on the rolls at the lower benefit levels.

Social Security subcommittee Chairman J. J. Pickle (D-Tex.) said he hopes to put the bill before the Ways and Means Committee "before Easter" with the goal of achieving final House and Senate passage this years.

Although the final bill approved unanimously by the Pickle subcommittee wash't exactly what Carter sought, Social Security Commissioner Stanford Ross said he is happy with the subcommittee bill and believes it would "make substantial improvements" in present law and administration.

The main purpose of the bill is to curb the rapid growth of the disability program, which takes care of persons below retirement age but too disabled to work. Since 1970 the number of beneficiaries has doubled and annual outgo has risen from $3.3 billion to about $15 billion.

Critics of the program have charged that under existing formulas, monthly benefits sometimes exceed 100 percent of what the disabled person earned before illness, because he gets benefits for a dependent wife and children as well as for himself. This encourages malingering, they charged.

The subcommittee voted yesterday to impose a "cap" on total family benefits. Under the bill, they cannot exceed 80 percent of predisability earnings or 150 percent of the worker's basic benefit, whichever is lower. It also voted to reduce the number of lowearning years that may be dropped out of the calculation of what the worker's average predisability earnings were. Like the cap, this will reduce the benefit calculation.

To encourage those on the rolls to try going back to work, the subcommittee voted to allow automatic reinstatement for a worker within one year if he leaves but then finds he really can't work; deduction of disability-related work expenses from earnings-eligibility levels, and cancellation of the two-year waiting period for reinstatement to Medicare benefits for a worker who leaves the rolls but then must go back.