A home ownership subsidy proposal for moderate-income families - directly financed by placing mortgage interest and property tax deduction limits on those with much higher incomes - is under consideration by the Department of Housing and Urban Development.

The program is similar to one proposed in a study on alternative mortgage instruments made by Raymond Struyk, now deputy assistant secretary for research and demonstration at HUD, and James Follain, a former college of Struyk's at the Urban Institute. The study was conducted with a grant from the Ford Foundation and published last month.

The Carter administration and Congress have expressed concern over the growing inability of young families to afford a first home, now that the median price is approaching $50,000. (At the same time, the White House is studying tax reform proposals that include placing limits on home owner deductions.)

Four years ago more than half of all the houselords buying houses were doing so for the first time. Today, according the Federal Home Loan Bank Board, 65 per cent of the homes are bought by families trading up, using the equity in their first home to buy a second or third.

The Follain-Struyk proposal would enable about 24,000 additional young households with annual incomes between $8,000 and $13,000 to become home owners each year. If this 10-year subsidy became fully operational, its would cost about $600 million a year.

To pay for this, a $3,500 ceiling would be set on the amount of mortgage interest and property taxes a home owner could deduct from federal income taxes. Revenues could amount to as much as $850 million annually, a figure that would expected to decline as wealthy home owners put their money into other tax shelters.

Four-fifths of the funds would come from home owners earning more than 30,000 a year, the researchers said; another 17 per cent would come from those in the $15,000 to $30,000 income range.

The program is suggested as a replacement for HUD's Section 235 home owner subsidy program, which acquired a bad reputation when many of its low-income beneficiaries defaulted on their mortgages. Section 235 has cost $170 million and helped 339,000 households, about the number that would be helped under the newer plan.