As home prices soar, congressional committees dealing with housing are near agreement on a plan to lower the down payment on popular graduated-payment mortgages.

House-Senate conferees are working out a type of graduated mortgage that would be easier for thousands of home buyers to afford. On such mortgages monthly payments increase over time, presumably along with the buyer's ability to make payments.

Such mortgages aren't new. The Federal Housing Administration has been insuring them since 1977, and many new FHA mortgages permit graduated payments. But lower down payments are needed, a Senate Banking Committee analysis asserts, because current requirements "price these mortgages beyond the reach of many young families."

For example, the buyers of a $55,000 home using the current plan would pay $4,200 down. The pending proposal, recently passed by the Senate as part of a comprehensive housing bill, would lower that figure to $2,500.

Although the House didn't include such a program in its housing bill, some version is expected to emerge from the conference deliberations. The ranking members of the Senate Housing subcommittee, Sens. Harrison Williams (D-N.J.) and Jake Garn (R.-Utah), "view it as a priority," one staff member says.

House conferees have resisted any new housing programs, but last week indicated they were willing to consider the new mortgage plan with some limitations.

As passed by the Senate, as many as 20 percent of all new FHA-insured mortgages could use the new graduated plan, or an estimated 80,000 to 100,000 mortgages a year. The house has proposed that the level be cut to 10 percent of new FHA mortgages.