Boston Properties is asking the Fairfax County Planning Commission to delay public hearings and action on a proposed change in the county's comprehensive land plan that could lead to construction of a 170-acre office park along the Dulles toll road at Hunter Mill Road.

A public hearing on the attempt by Boston Properties to change the Fairfax County land use plan for the area at the southeast corner of the interchange near Reston is scheduled for Thursday.

But Tom Hutchinson, vice president of the Boston-based land development company, which has an office in Springfield, said that his firm is asking for the deferral so that it can reevaluate the impact of the new Dulles toll road on traffic conditions.

Boston Properties would like to build a corporate office park with 2.25 million square feet of space in 17 buildings on the site.

Hutchinson said rumors that his company is backing away from the project are unfounded. "Boston Properties is still totally committed to this project," he said.

"If we do not get the extension, we would withdraw and file again immediately," Hutchinson said. Such a move would buy the time his company says it needs to review what impact the opening of the Dulles toll road would have on traffic patterns near Hunter Mill Road.

The land involved in the requested change is zoned residential. The county's land use plan calls for construction of single-family detached homes on such a site. Almost a year ago, Boston Properties filed an application to amend that plan to change the site to an industrial status.

Fairfax County's land use plan is the so-called bible of comprehensive planning for Fairfax. The process by which it can be changed is complicated. Before the site can be rezoned to allow office construction, the land plan has to be changed. But such a change would not automatically guarantee approval of Boston Properties' application or any other application, explained a county staff member.

"If and when the plan is changed, the whole rezoning process would begin at ground zero," he said.

The effort to change the land plan has angered some residents of the area who say the recent construction of single-family homes nearby proves that the land can be developed economically for residential purposes. Residents also have expressed anger about traffic that would be generated by the proposed office park.

Homeowners in the area have opposed the change at several community meetings, complaining that Hunter Mill Road and nearby Sunrise Valley Drive already are overcrowded. Hunter Mill Road is a winding, two-lane rural road that runs between Oakton and Reston and picks up heavy traffic from Lawyers Road, another commuter artery.

If the planning commission fails to delay next week's scheduled hearing, Hutchinson said his company simply would withdraw the application. Boston Properties then would reapply in November during the time set aside each year for filing amendments to the land use plan. If amendments are not filed during that particular period, applicants must wait a full year before filing.

This year a citizens task force said Boston Properties' application was significant enough to treat separately from other amendments filed. Under Fairfax County's system, every amendment filed in every third year must be heard. Next year, 1985, is one of those "third years," so if Boston Properties withdrew the application next week and refiled next month, it would not lose any ground.

Amendments filed in the two intervening years must pass "strict urgency tests" to be considered by the planning commission and the board of supervisors.

But Hutchinson hopes to get the extension from the planning commission. New traffic studies produced by Kellerco, a McLean-based traffic consulting firm, have just been completed, Hutchinson said.

"With a toll road just opening, we need to make sure anticipated traffic pattern changes take place. We need time to verify, to take some actual counts," he said. "We're going to see some diminishing problems at important problem areas," he predicted.

"We hope to spend more time with the county's transportation and planning staffs that are involved," Hutchinson said. He added that he has spent many hours alone driving on the Dulles toll road since it opened to measure the time it takes to get from one site to another along the road.