SEATTLE - Volunteers in Washington and across the country will spend one night this week counting and surveying homeless people - on the streets, in shelters and soup kitchens, and even in jails. In last year's one-night count, the Washington total was almost 23,000. About one-third of the homeless said they were veterans.

President Obama and Gen. Shinseki, who heads the Office of Veterans Affairs, recently announced they have 'zero tolerance' for homelessness among vets. But Neil Donovan, executive director of the National Coalition for the Homeless, says it's a population that is not easy to serve - and sometimes, not easy to find.

"Many veterans don't go into shelters. They're shelter-resistant; they have the ability to stay out in tent cities and encampments. So they're going to be a hard population to enumerate. But if your goal is 'zero tolerance,' you're obligated to find out what that number is."

The one-night count is used by the federal government to develop housing policies and allocate money for service providers to the homeless. Critics say it is unscientific, depending on such factors as the weather on the nights of the count. Donovan calls it an important tool nonetheless.

"If we are to aim towards the goal of ending homelessness, with the assumption that it is caused by a lack of affordable and accessible housing and jobs that pay a living wage, we need to know what the size of the population is."

Donovan is also concerned that this year's count won't reflect a growing category of homeless people: those staying with relatives or friends temporarily, after a foreclosure or job loss. Including those people, the Washington State Coalition for the Homeless estimated last year's statewide total at 102,000.

Most cities do their one-night counts this week on Wednesday or Thursday. The results should be released this spring.