Congressional negotiators and the Clinton administration are close to agreement on legislation that would allow public housing authorities to put more working families into apartments that in recent years have been reserved almost exclusively for the very poor.

The change has been sought by officials in many cities who contend that large concentrations of extremely poor people in public housing projects have shattered neighborhoods, sapped their commercial vitality and left them devoid of stable families.The changes would free housing authorities to set aside hundreds more vacant units each year for families making as much as $40,000 a year. New York City's housing authority considers the bill a necessary first step toward creating a marketing strategy designed to encourage higher-income families to move into its housing projects.

The legislation is also expected to give housing authorities greater flexibility in setting rents on the nation's 1.2 million public housing units, authorize mayors in some cities to take over poorly run housing authorities and allow low-income people to use federal housing vouchers to help pay the costs of buying a house.

The public housing bill has been pressed mainly by congressional Republicans over the opposition of Democrats and Housing and Urban Development Secretary Andrew Cuomo, who have said that the Republican bill would leave poor people without housing. But Cuomo has negotiated changes in the bill that have made it acceptable to many Democrats.

Cuomo is also on the verge of winning enactment of two other housing measures that are likely to make it easier for congressional Democrats and the Clinton administration to accept the public housing bill.

One would create about 15,000 new Section 8 housing vouchers, which are federal rent subsidies for low-income tenants. If approved, the increase would be the first in about five years. Nearly 3 million households now receive housing vouchers. The second would make federally insured mortgages available to at least 17,000 more home-buyers a year.