There’s a one-word explanation for why there are far fewer mentally ill men and women living on the streets today than there were just five years ago: Housing. Since the late 1980s, New York has created nearly 13,000 new beds in community-based residences for homeless, mentally ill men and women, the majority of them in the city.

That pace of development is coming to a halt as funding runs out. The nonprofit groups that run the existing housing say their residences are filled to capacity.

“It’s much harder to place people now,” says Steven Coe, executive director of Community Access, an organization that houses hundreds of the mentally disabled on the Lower East Side. “Our intake is a trickle because we don’t have space.”

In 1990, state and city officials signed a five-year agreement to provide permanent housing to more than 7,000 homeless. But in 1994, Governor Pataki canceled the final 300 units and the agreement expired soon afterwards. The last units in the pipeline are scheduled for completion this spring and so far, neither Giuliani nor Pataki extended the effort.

Yet in 1993, the state Office of Mental Health estimated the city needed housing for at least 14,000 more mentally ill homeless people.

Brooklyn Assemblyman Jim Brennan and a group of advocates are pushing Albany for new capital to develop 2,000 rooms in supported, single room occupancy-style buildings. The group, which includes the Coalition for the Homeless, Community Access and several other organizations, is also calling for new rent subsidies to move thousands of people from community residences into private apartments.

Recent research has found that a majority of the city’s shelter beds are used by a relatively few needy men and women, many of them mentally disabled, who could be housed far more cheaply in supported housing. This could free up shelter beds for the thousands of short-term homeless who need a place to stay.

Last month, as shelters for singles reached peak capacity of 7,400, the city prepared to open a new shelter for 380 men in Central Brooklyn for $6 million.

Albany, however, is not likely to move quickly, if at all. “I’d be surprised if we could pull together a new agreement before June,” says Shelly Nortz of the Coalition for the Homeless.

Still, there’s a need to move fast. “I’m approaching gridlock,” says Peter Campanelli, president of the Institute for Community Living, the largest provider of housing for the mentally disabled in the city. “I’m down to the last five or six supported housing vacancies out of more than 200. I have to hold people in transitional beds that are more expensive because there are no apartments for them. I’ve never had to do this before.”

The Governor’s office failed to return calls on the issue. A spokesman for Mayor Giuliani had no comment.