A handful of residents, in their first official look at proposed changes to their neighborhoods along Columbia Pike in Arlington County, expressed concerns Saturday about whether the planned addition of thousands of new apartments will overwhelm their small single-family-home areas.

The Arlington County Board, in setting a July 21 public hearing on the Pike’s long-awaited housing plan, learned that as many as 6,000 new rental units could be added to the stock of 9,000 apartments there over the next 30 years. The county hopes to preserve 4,500 of them as affordable housing.

The area is home to about one-quarter of the county’s affordable rental housing, county staff said Saturday, and their goal is to retain the same number, although they admitted that will be a challenge. The first challenge at Saturday’s board meeting came from homeowners in the area.

“I’m concerned our home will be overshadowed by an apartment building right next door,” Maire Gee, who lives along 12th St., said.

“This has the potential to drop high-density multifamily housing into a neighborhood of single family homes,” said Brenda Cox, representing the Arlington View Civic Association, which asked the board to delay their vote until October.

The Columbia Pike housing plan is aiming for denser, pedestrian- and transit-oriented neighborhoods with more vibrant commercial and office uses along the street’s 4.5 miles from just over the Fairfax County line to the Air Force Memorial near the Pentagon. Now an eclectic mix of strip malls, ethnic eateries and nonprofit headquarters, Columbia Pike has a combination of garden apartments, condos and single family homes; the street itself is often overwhelmed with stop-and-go car and bus traffic.

The County Board would like to transform the area into a greener streetscape and lure old and new residents into using transit. The housing plan is part of a bigger Columbia Pike initiative that has been underway since the late 1990s. The controversy over whether the county should build a streetcar line there, or opt for articulated “bendable” buses is part of the separate transit plan.

Virginia landowners, who don’t have to provide low-cost housing, have the option of redeveloping their property according to the present zoning. But the county is dangling another option, allowing them to create denser, taller and more lucrative structures if they agree to abide by certain rules, such as the orientation of the buildings, adding green space and setting aside 20 to 25 percent of the units as “affordable housing.”

What affordable means varies with family size and income, but a family of four could have an income of up to $64,000 to qualify for most, and up to $86,000 to qualify for others. But it’s no sure bet that the thousands of families who make that much, or less, would be able to get into those apartments.

The county hopes that with its offer of higher density, as well as financial and tax incentives, loan programs and the ability of developers to transfer development rights, 3,000 of the 4,500 existing affordable apartments will be retained.