I am surprised and disappointed by The Post's endorsement of changes to Initiative 17 -- the Overnight Shelter Act {"Rewriting the D.C. Homeless Law," editorial, May 23}.

The heart of that act is the principle that every needy person is entitled to decent overnight shelter. As a lawyer who specializes in low-income housing I know that meeting that obligation has been expensive because the D.C. government has used profit-oriented rather than nonprofit shelter providers and because the D.C. government has not used the 2,619 city-owned public housing units that now stand vacant, 302 of which require only minor or moderate repair.

It is no answer for the District to eliminate the entitlement and to limit shelter stays to 30 or 90 days. What the District must do is shelter people until housing is available to them. For low-income people, subsidized housing is absolutely essential.

A report prepared by Cushing Dolbeare for the Low Income Housing Information Service titled "Out of Reach: Why Everyday People Can't Find Affordable Housing" points up the need for subsidized and affordable housing. According to the report, two persons working full-time at the minimum wage do not earn enough to pay the HUD-established fair market rents for the District. The fair market rents are $570 and $670 for one- and two-bedroom units respectively. The net hourly wage needed to rent such units at 30 percent of income would be 327 percent and 385 percent of the minimum wage. Aid to Families with Dependent Children provides even less: the maximum monthly AFDC grant in the District in 1989 was $393 for three persons and $480 for four. The fair market rents -- $570 and $670 -- far exceed the full AFDC grants.

Forty percent of the renter households in the District cannot afford the fair market rent for a one-bedroom apartment; 46 percent cannot afford the fair market rent for a two-bedroom unit. What is a serious housing problem for those near the median is a crisis for those dependent upon minimum-wage jobs and public assistance. The District government could house these people decently, if it would use intelligently the resources it already has. This is what The Post should be urging. FLORENCE WAGMAN ROISMAN Washington