Gov. John N. Dalton said last week that a four-lane bypass planned to solve the mounting traffic volume that has saturated the main roads of southern Fairfax County "is a major priority in the Northern Virginia area."

But, Dalton said, construction of the Springfield bypass probably will not begin until 1980. County officials says the bypass is their "number one" priority in future road construction.

At a press conference in the Massey Building in Fairfax County, Dalton said he was taking a helicopter ride along the planned route so he could get a "first-hand view" of the area. Waverly L. Brittle, a state highway official, and Fairfax County Board of supervisiors Chairman John F. Herrity joined Dalton on the helicopter tour.

The bypass, which includes three main sections, would extend from Rte. 7 in the Dranesville area to Rte. 1 at Lockheed Boulevard.

County officials have urged that the bypass be built to provide better access to the growing southern and western parts of the county and to alleviate heavy traffic congestion on the already over-utilized secondary county roads in the area.

Fairfax County is experiencing a population surge, most of it in the south and west, and county roads have not been adequate to handle the accompanying traffic increases.

A total of nearly 48,000 people will be added to the county's present population - 567,600 - this year and next, according to a newly released county study.

The Springfield bypass is expected to provide better access to the Reston-Herndon area, the Rte. 1 corridor form Springfield, the Springfield-Franconia Metro station and the Pohick area, where about 40 percent of population increases projected for 1978 and 1979 is predicted to be concentrated.

The proposed bypass also is expected to bring relief to the heavily traveled Keene Mill Road in the Springfield area - a familiar route for commuters to the District.

It is also expected that the bypass will help to promote economic development near Dulles International Airport.

According to county transportation director Shiva Pant, about half the work on the bypass would involve construction of new roads, while the remaining half would involve improvements to existing secondary roads.

He said about 10 percent of the total right-of-way needed for the route already has been acquired by the county.

Of that, 40 to 60 percent has been acquired for the section between Rte. 123 and 1-95, he added.

A few weeks ago, the county Board of Supervisors authorized a private consulting firm to study the proposed route.

Dalton said using the private consultant prevents the county from being forced to wait several years for the state highway department to conduct the studies.

County and state transportation officials have estimated that it will take eight to 10 years to build the bypass, which is expected to cost about $80 million.

The bypass will be built in stages, according to Pant. He expects that Lockheed Boulevard and Van Dorn Street section to be the first to be built.