Construction crews continue to work on building the Arlington Mill Residences at Columbia Pike and Dinwiddie St. in Arlington on Friday. (Patricia Sullivan/The Washington Post)

In a display of the demand for affordable housing in Northern Virginia, more than 3,600 people have applied for a chance to rent one of 122 new affordable apartments still under construction along Arlington County’s Columbia Pike.

The volume of applicants surprised even the nonprofit developer of the Arlington Mill Residences. Hundreds of people were expected to seek a spot in the complex via lottery, but on the first of four days that the waiting list was open, they began lining up before dawn. By 6 p.m., 949 people had applied.

Nina Janopaul, president and chief executive of nonprofit developer Arlington Partnership for Affordable Housing, called the outpouring of interest “a case of a dramatic rise in demand for affordable housing in the close-in area.”

The new construction on Columbia Pike, next to a new community center, she said, proved highly desirable.

The increasing cost of living in the inner suburbs, especially in northern Virginia, has taken a significant toll on the number of apartments considered affordable to families. In 2000, about 20,000 of the 35,000 rental apartments in Arlington were ranked as market-rate affordable; now, only 6,000 of the county’s 43,000 rentals are.

Those who lined up early last week for the chance at the new apartments attested to the difficulty of finding affordable rentals.

“I pay $1,600 for a one-bedroom” on the west end of Columbia Pike, said Senait Worku, a coffee shop cashier who works two jobs, as does her husband. “We have lived here seven years, and we want to try for lower rents.”

Among the taxi drivers, computer techs and disabled senior citizens, a pregnant Melkam Tebeje turned up at the rental office with several members of her family.

“We need to have an apartment without paying a lot of money,” she said. An Alexandria grocery store cashier, Tebeje said she can’t save for school because her rent is so high. “If I get one of these [apartments], I can go to school, too, but now I don’t have time because I work two jobs.”

The four-story apartment building, at 901 S. Dinwiddie St. just behind the newly opened Arlington Mill Community Center, will be affordable to people or families earning less than 60 percent of the area’s median income, which would mean a family of four with an income of $64,000 or less could qualify. Most of the apartments have two or three bedrooms. A dozen of the units will be set aside for those with very low incomes, and another dozen are wheelchair-accessible apartments. A wing with eight efficiency units has been set aside for those who are the very hardest to house, such as the homeless, APAH officials said.

APAH’s Janopaul said the high demand is not restricted to Arlington Mill.

“We have a huge waiting list at our Parc Rosslyn [building], but they didn’t apply all at once,” she said.

Local and state governments have been trying to subsidize the creation and preservation of apartments for area residents, because pushing the non-affluent to outer suburbs exacerbates the Washington area’s traffic congestion and because many communities value a mix of people who earn a variety of incomes.

The $31 million Arlington Mill Residences are being financed with an $8.9 million loan from Virginia’s low-income housing finance agency, and with $22 million in federal tax credit housing money from Bank of America. It sits atop a parking garage, built with a loan from Arlington County that’s since been repaid. The property is on land owned by the county and APAH has a discounted 75-year lease.

The demand for the rentals “is amazing, no question about it,” said J. Walter Tejada (D), chairman of the Arlington County Board, who made increasing affordable housing the board’s top priority this year. “At the same time, it doesn’t surprise me. It validates the challenge that we recognize and we have to meet. . . . These are not giveaways. We make loans, we work with developers — this is how we do affordable housing in Arlington.”

Half of all four-person family households in the Washington region this year earned more than $107,500; half earned less, including beginning teachers, police and firefighters, retail employees, construction workers and many professionals. Most are priced out of the home-purchase market and often struggle to find adequate rental housing. The average rent in Arlington last year ranged from $1,422 per month for an efficiency to $2,782 for a three-bedroom unit, the county reported, rising 13 percent from 2011.

Affordable housing advocates say that the situation has been getting worse over the past decade and is now a crisis.

“If you are not safely and decently housed, it’s hard to hold a job, it’s hard to do well in school, and you are more likely to have health issues,” said Michelle Krocker, executive director of the Northern Virginia Affordable Housing Alliance.

APAH and its construction partner are still sorting through the applications, entering them into a spreadsheet and determining how many of the 3,600 applicants qualify for the Arlington Mill apartments. The lottery to award the units is expected to be held late next week.