Maryland residents have until Jan. 31 to apply for refunds of illegal rent increases they paid four years ago at certain federally subsidized housing projects.

Although the average refund is $500, many residents have failed to apply.

The refunds are part of a $60 million settlement between the Housing and Urban Development Department and a legal services lawyer who filed a class action suit in 1975.

Persons who lived in so-called HUD Section 236 housing between Feb. 1, 1975 and Sept. 30, 1977, may be eligible for the refunds.

In Maryland, tenants in 12,932 units were overcharged. But by last week, only 13 percent of those eligible had applied for the rebates.

Claim forms can be obtained from Section 236 project managers or by calling, toll free, 800-824-7980.

Persons who lived in the following projects at the time may be eligible: Montgomery County Amity Gardens, Bauer Park Apartments, Emory Grove Court, Friendly Gardens; Georgian Court Apartments, Great Hope Homes.

Leafy House, Manor Town, Montrose House, Park Montgomery, Rebecca, Rock Creek Terrace, Stewardtown Homes.

Suburban Park Village, Towne Center Apartments, The Willows. Prince George's County arnold Gardens, Birchwood Garden, Capital Towers, Capital View, Section I & Section II.

Crest Apartments, Eastern Avenue Apartments, Imperial Gardens, Kimberly Gardens, Section I, Laurelwood Mutual Home, Millwood Townhouses, Nalley Apartments, Park 16 Apartments, Quincy Village.