Loudoun County supervisors are protesting a state highway department decision that they charge will necessitate a signal-controlled intersection at the Rte. 28 interchange with the Dulles Toll Road and cause massive traffic tie-ups.

County officials say the interchange plans, which call for a diamond-shaped access rather than a full cloverleaf, threaten to disrupt their plans to develop the county's Rte. 28 corridor by discouraging developers, who would be reluctant to buiild along a road where traffic tieups are likely.

". . . An incomplete instersection at the toll road, with traffic lights at the top of each exit ramp, . . . would create a real bottleneck," particularly because the county wants to widen Rte. 18 to four lanes and eliminate all its stoplights, said William Keefe, Loudoun's chief planner.

Virginia Department of Highways and Transportation officials, however, say their plans for the interchange were finalized six months ago and are unlikely to change because of budget constraints. Construction on the toll road has been underway for a month and is scheduled to finish in 1984.

"I haven't heard anything about this [protest]," said Donald Keith, the highway department's division administrator for Northern Virginia. "We have no plans to fund a full coverleaf [at Rte. 28] and, if we were changing the plans, I would know about it."

Loudoun officials are particularly upset because they said they first heard of the final design plans when a Fairfax County real estate agent tipped them off a month ago. It was then that they said they learned that plans called for a diamond-shaped interchange in which some vehicles on Rte. 28 will have to cross oncoming lanes of traffic to gain access to the toll road while other vehicles exiting the toll road to turn left onto Rte. 28 will be forced to wait for traffic to clear.

A cloverleaf would give commuters access to the toll road and Rte. 28 in all directions without forcing traffic to come to a stop, they said.

Expanding Rte. 28 to four lanes is the county's second highest priority in highway projects. Top priority is making Rte. 7 west of Leesburg four lanes.

"It [Rte. 28] will be a free-flowing road, with the capacity to handle about 61,000 cars a day." Keefe said.

Expanding Rte. 28, however, is not included in the state highway department's six-year list of projects, and many officials involved in designing the toll road were unaware of Loudoun's plans to push the road as a priority, officials there say.

Neither can Loudoun count on support from Fairfax County.

"Just redesigning the diamond to a cloverleaf won't solve the traffic problem if you merge into a road where there is already stop-and-go traffic," said Shiva Pant, Fairfax County's transportation director. "The only cloverleaf on the toll road will be at Route 7. They don't need a coverleaf at Route 28."

But Loudoun's board members say they will fight for making Rte. 28 a limited access anyway.

"Four-laning Route 28 and putting in a cloverleaf is crucial because we have planned 28 to be an industrial corridor," said Loudoun County Supervisor Betty Tatum (D-Guilford). "The road is already having a terrible backup from commuters now using the Dulles Access Road. It will be much worse when the toll road opens, and it won't be very inviting to developers if it's not up to standards."

County planners expect the population of eastern Loudoun to double within the decade, and they believe most of the residents will plan to commute down Rte. 28 and the toll road to jobs in Fairfax County and Washington. The planning office estimates that by 1990 Rte. 28 will be carrying 100,000 cars a day.

The Loudoun board has asked Highway Commissioner Joseph Guiffre of the Culpeperdistrict to talk to other members of the state Highway Commission about the problems they anticipate on Rte. 28 when the toll road opens.

Guiffre said his position was to support decisions that make long-range needs easier to meet, but that he couldn't guarantee a solution.

"I'm sure there is not money in the regular highway fund for this cloverleaf," Guiffre said. "To build it, it would have to be tied into the toll-road bond issue funds."

Highway officials administering the construction of the toll road say most of the funds raised by the bond issue already are earmarked.

"There are no funds to build it [a cloverleaf at Rte. 28] at this time," Keith said. "There is only $57 million in the fund from the bond issue."

"The county is not in a position to be able to pay for that kind of improvement itself," said Loudoun's Keefe. "And I hope we won't get stuck doing it in the future because within 10 years we will need that cloverleaf."