Tracy Jones of the Compass Center, a Seattle agency that has seen a handful of new homeless each month, said she was surprised by “the quickness in which Iraqi Freedom veterans are becoming homeless” compared with the Vietnam era. The availability of meth and crack could lead addicts into rapid downhill spirals, Ms. Jones said.

Poverty and high housing costs also contribute. The National Alliance to End Homelessness in Washington will release a report on Thursday saying that among one million veterans who served after the Sept. 11 attacks, 72,000 are paying more than half their incomes for rent, leaving them highly vulnerable.

Mr. Dougherty of the V.A. said outreach officers, who visit shelters, soup kitchens and parks, had located about 1,500 returnees from Iraq or Afghanistan who seemed at high risk, though many had jobs. More than 400 have entered agency-supported residential programs around the country. No one knows how many others have not made contact with aid agencies.

More than 11 percent of the newly homeless veterans are women, Mr. Dougherty said, compared with 4 percent enrolled in such programs over all.

Image Joe Williams lives in a homeless shelter in Washington. Credit... Brendan Smialowski for The New York Times

Veterans have long accounted for a high share of the nation’s homeless. Although they make up 11 percent of the adult population, they make up 26 percent of the homeless on any given day, the National Alliance report calculated.

According to the V.A., some 196,000 veterans of all ages were homeless on any given night in 2006. That represents a decline from about 250,000 a decade back, Mr. Dougherty said, as housing and medical programs grew and older veterans died.