The Arlington County Board will decide Saturday whether to significantly expand its goals for affordable housing over the next 25 years by requiring nearly 1 in 5 residences to be within the financial reach of low- to
moderate-income households.

The plan, three years in the making, is the latest attempt by lawmakers to ensure that at least some housing in the increasingly expensive Northern Virginia suburbs remains affordable to starting teachers, food preparers, retirees and others who make 60 percent or less of the area median income — about $65,000 for a family of four, or $45,900 for a single person.

In a county where the median income is $106,400 and the average single-family home is assessed at $790,600, the quest for more moderately priced housing can be frustrating. In 2013, just 9 percent of the county’s housing stock was affordable to low and moderate earners, compared with 26 percent in 2000.

Officials in the District, Fairfax County, Montgomery County and Alexandria have adopted affordable-housing programs in recent years, with varying degrees of success.

“This is a regional problem,” said David Cristeal, Arlington’s housing director. “We want to help each other meet this regional need.”

Arlington’s plan would add about 15,800 affordable units to the county’s stock of 10,000, making 17.7 percent of county homes affordable to low- and moderate-income households by 2040.

Many of the affordable units are expected to be older homes or apartments, which don’t appreciate as quickly as newer places. The plan calls for distributing affordable housing, which is concentrated mainly in South Arlington, more evenly throughout the county.

While most of the attention is focused on renters who make less than the median income, rising prices also affect those who are trying to buy a home, officials say.

For that reason, Arlington’s plan calls for keeping 28.4 percent of the new homes built in the county by 2040 affordable to buyers whose incomes are between 80 and 120 percent of the area median — between $85,000 and $127,700 for a family of four.

The 150-page plan is expected to pass, but it will probably be amended during the board meeting. It includes details about how to achieve the goals of more and better dispersed affordable housing, but there is no estimate of how much the county will have to spend to make that happen.

In new language added just Thursday, the plan specifies that it “does not commit the County to any immediate or future expenditures.”

Money to support affordable housing primarily comes from the county’s annual budget, which is subject to board approval each year. Arlington, which began helping finance affordable housing in 1987, devotes 5 percent of its budget to housing efforts, Cristeal said. The county allocates about $8.5 million a year in direct grants to families, $12.5 million for an investment fund that lends money mostly to nonprofit developers, and $5 million to $7 million for property tax relief.

A recent study by the Greater Washington Housing Leaders Group said that at least four strategies are needed to address the growing need for less-expensive housing: increasing the sources of capital for construction of affordable housing, increasing the availability of land for such housing, reducing the cost of development, and generating political will.

“Ultimately, affordable housing must be seen as a fundamental component of an economically healthy region, no less important than water, sewers, and public transportation,” author Rick Cohen wrote.

His report, like one last year by the Urban Institute, urges local governments to pay more attention to the needs of those who make less than half of the median income. It is the same point that the advocacy group Virginians Organized for Interfaith Community Engagement has made repeatedly in its appeals to Arlington lawmakers.

“The faith traditions that we represent, while very different, are entirely consistent in their recognition of shelter as, not only a basic human need and a fundamental faith and ethical precept, but also indispensable to the sustainability of family and community,” the group wrote in a letter to the board this week.