Fairfax County officialsannounced yesterday a package of 12 road improvements, valued at $44.8 million, that they are urging be included in a proposed road bond referendum this fall.

The projects, coupled with a $89.5 million proposal to fund two segments of the cross-county Springfield Bypass, comprise a $134.4 million bond proposal. If approved by the county supervisors Aug. 5, it would be the largest single bond package ever presented to voters in the county.

"It's historic," said Fairfax County Executive J. Hamilton Lambert. "I think it's a good package, in line with what most of the citizenry wants."

The bond proposal represents an ambitious plan that county officials hope will provide a measure of relief at the bottlenecks and clogged intersections that bedevil commuters all over the sprawling county.

All but one of the 12 projects announced yesterday would entail major construction to widen or improve existing roadways around the sprawling county. The other project -- the most expensive of the package -- calls for building a $13.2 million extension of South Van Dorn Street to link it to Rte. 1 in southeastern Fairfax. The least costly of the proposals calls for $470,000 to improve an intersection of Leesburg Pike (Va. Rte. 7) and Baron Cameron Avenue in the Reston area.

Four of the 12 projects proposed by the county staff -- representing about $22 million -- would fund road building in the county's Lee District, a section of Fairfax south of Alexandria that has some of the county's oldest neighborhoods and particularly severe road congestion.

"We have a terrific amount of traffic in the southern end of the county," said Lee District Supervisor Joseph Alexander, the county board's senior Democrat. "I don't think there's any secret that these are areas that need attention."

County officials have recommended building two segments of the Springfield Bypass, one between the Dulles Toll Road and Rte. 50, the other from Rolling Road across I-95 to Beulah Street near Franconia.

Conspicuous by its absence from the package is funding to improve Sully Road (Va. Rte. 28), the two-lane road that slices across western Fairfax from Dulles International Airport to the Prince William County line. The Rte. 28 corridor is the focus of intense development by high-technology firms, particularly in the Dulles area where the state is building its Center for Innovative Technology. The road, already badly clogged at rush hour, is considered seriously inadequate to handle traffic expected in the next decade.

County officials said they were reluctant to include money to widen Rte. 28 in their proposal without funding from private developers, the state highway department and Loudoun County. "What benefit is there for Fairfax County if Loudoun County does nothing?" said Denton U. Kent, deputy Fairfax county executive for planning and development. Kent said Loudoun officials are balking at proposing a bond issue for road building, a responsibility that has traditionally been borne by the state government.

The Fairfax supervisors are scheduled to take up the staff proposals Monday, and on Aug. 5 they are scheduled to formulate a final bond package to send on to county voters Nov. 5. If approved by a majority of county voters, construction could begin by 1988.

County officials said the supervisors may add some smaller projects to the bond package but are unlikely to eliminate any of the staff proposals. They added that the $134.4 million package is below the ceiling of debt that the county can incur. Some supervisors, notably Audrey Moore, the Annandale Democrat, have questioned proposing such a large referendum, fearing that it may jeopardize the county's coveted AAA bond rating.

County officials said that the current bond package is the first of what could amount to several large bond proposals. The $89.5 million earmarked in this package for the Springfield Bypass would pay for less than nine miles of the 35-mile road, which would sweep from Rte. 7 in the north to Rte. 1 in the south.