PORTLAND – The primary homeless shelter in Maine’s largest city is so crowded it has turned away people with no place else to go for shelter for the first time since its creation 12 years ago.

The Oxford Street Shelter overflowed twice in the last few weeks, and the situation could soon get worse.

There are dozens of people sleeping outdoors by choice who may soon decide to come in out of the cold, officials say.

The executive director of the Bangor Area Homeless Shelter said overcrowding has not been a problem there yet.

“The availability of affordable housing is much worse down in that area,” said Dennis Marble of the Bangor shelter. “We’re not running into what Oxford Street in Portland is. … It’s still mostly business as usual here.”

But in Portland, city officials and advocates for the poor are searching for solutions including finding space for overflow beds and intensifying their search for vacant rooms and apartments in a tight housing market.

“This community has repeatedly, year after year, made a commitment that nobody needs to sleep outside, and I think we’re facing a big test,” said Mark Swann, director of the Preble Street Resource Center and soup kitchen.

Oxford Street is the city’s primary shelter for adults. It opened in 1989 with an official capacity of 50 people. It was repeatedly expanded and can now hold 154, a number that seemed out of reach only a few years ago.

Portland’s homeless population has been growing rapidly for the last three years as the prosperous economy and lack of apartment construction pushed rents out of reach for poorer residents in southern Maine.

October is historically a peak time at the city’s shelter because cool nights bring more homeless people inside. This year, city officials said, more migrant workers have come through Portland’s shelter on their way to work picking blueberries, potatoes or apples.

Officials also said there has been an apparent increase in the number of people who abuse alcohol or drugs on the city’s streets. Intoxicated men are sent to the Milestone Shelter, but that facility also has been full and has been sending its overflow to Oxford Street.

In recent years, the Oxford Street shelter switched from army-style cots to floor mats, partly because they take up less space and allow for more beds.

“The mats are pretty much one on top of the other,” said Cliff Metzler, who recently came to Oxford Street from a shelter in Brunswick.

The crowding adds to the depression and stress that can keep some homeless people from working their way back to independence, said Joan Redding.

“There are 150 people sleeping on the floor, side by side. Some of them are sick. I had two hours sleep last night,” Redding said.

Demand for the beds has met or exceeded capacity six times in the past month, said Gerald Cayer, director of Portland Health and Human Services Department.

On some of those nights, the staff made phone calls and found beds in some of the smaller, privately run shelters around the city that serve intoxicated men, teen-agers and women. Those shelters also are more crowded, however, and on two of those nights homeless adults were forced to leave the Oxford Street shelter with nowhere else to go, Cayer said.

City officials are hoping to ease the crisis by using every empty bed at the private shelters and by working harder to shrink the homeless population.

“It’s all well and good to have an overflow plan, but it’s not helping us address the issue of homelessness,” Cayer said.