PORTLAND – A referendum to limit growth in Portland could put the squeeze on an already tight housing market.

“I know we do have a big problem with housing,” said Diane Manzi, a Portland resident who said her rent has doubled in the past 15 years. “But how much more can we develop? We’re so big.”

The referendum asks voters to stop most development until planners and residents complete guidelines for future housing. The effort will last through the summer.

The proposal also would require the city to give neighborhoods more influence in the development process, something for which residents have repeatedly lobbied.

But with apartments hard to find, rent prices through the roof and homeless shelters crowded with working people, affordable housing advocates say the referendum could add to the city’s housing crunch.

Portland has had a vacancy rate of only 1 percent to 2 percent in its 16,000 apartments for about the past year. Rents jumped by 289 percent between 1980 and 2000, while incomes increased by 132 percent, according to Michael Finnegan, executive director of the Maine State Housing Authority.

There are shortages throughout the range of housing, but the problem is most severe in the lower price range, as rental rates force more tenants into smaller and older units. As a result, more people are living in shelters, sharing substandard apartments or moving to the suburbs.

The referendum doesn’t make sense to Brenda Lopez, a Portland resident who says she struggles to make her rent every month.

“Why should I block [development] when we need more housing?” she said.

But those who support the referendum say it will, in the long run, create more affordable housing by forcing the city to plan better.

“I don’t understand how anybody who wants affordable housing would vote no,” said Jim Estes, who is helping to rally support for the referendum.

He said the rental crisis is evidence the city needs to make final its housing development guidelines immediately, and said passage of the referendum would speed up that process.

Some affordable housing advocates, however, cite language in the referendum that seems aimed specifically at blocking affordable housing. For example, they say, the proposed restrictions on development would ban temporarily projects with more than four units of publicly financed housing, but would allow as many as 19 privately financed units to go forward.

“That is a class-based distinction right there,” said Mark Swann, director of the Preble Street Resource Center, which helps find housing for poor residents. “To me, that’s very anti-poor people.”

A tight housing market is not unique to Portland. In Biddeford, there’s a two-year waiting list for Section 8 subsidies. And in Bristol, 60 percent of the people make less than $34,000 a year, but the average house costs $212,000, Finnegan said.