Although President Carter has asked Congress to cut back the $15-billion-a-year Social Security disability program in order to save money, the prestigious Social Security Advisory Council has recommended eligibility changes that could add several billion a year in costs to the program.

The advisory council's recommendations are only tentative and it may ultimately recommend delay on some of its proposals, but if enacted now, they would add $4.1 billion a year net to program costs. The thinking behind the recommendations is that some disabled workers or their disabled wives are simply not getting coverage under today's eligibility rules.

The advisory council is headed by Henry Aaron of the Brooking Institution, a former assistant secretary of health, education and welfare. It includes experts like former Social Security commissioner Robert Ball, leading economists like Joseph Pechman of Brookings, and Gardner Ackley, of the University of Michigan; Mel Glasser, United Auto Workers pension chief; Equitable Life Vice President Morton Miller and the AFL-CIO's Bert Seidman.

Here are some of the key recommendations which the advisory council recently outlined in a letter to the House Ways and Means Social Security subcommittee:

Reduce the waiting period for receipt of benefits from the current five months after onset of illness to three months. Cost: about $1 billion a year on a long-range basis.

Eliminate the requirement that a person must have worked in 20 of the 40 quarter-years prior to disability in order to receive monthly benefits. Instead, anyone who has worked 40 quarters at any time in his life would be eligible. Long-range cost: $2.8 billion a year. Ball, in a telephone interview, said this would probably be a recommendation for some years in the future, not for immediate action.

Make the disabled widow of a worker who had been covered by Social Security eligible for a full widow's benefit regardless of age-instead of a reduced benefit at age 50 or above, as at present. Cost: $300 million.

Make the disabled wife of disabled worker eligible for a wife's benefit regardless of age. At present, she isn't eligible. Cost: $400 million.

Ease slightly the definition of disability for workers over 55. Cost unknown.

The council endorsed some Carter work-incentive and review proposals which would save a net of $300 million a year. It and also endorsed Carter's concept of making sure family benefits don't exceed what the worker earned before going on disability, but with a looser ceiling that would save only $100 million a year instead of the )ight or nine times that in a bill approved by the House subcommittee.