D.C. transportation department director Douglas N. Schneider Jr. said last week in Senate testimony that the planned construction of I-66 from the Capital Beltway to Theodore Roosevelt Bridge in suburban Virginia would increase rush-hour traffic and parking problems in the District.

Schneider told the Senate District Appropriations Subcommittee he did not think plans to limit the four-land highway to car pool and bus traffic during rush hours would work in the long run.

"I don't think there are enough buses and car pools to justify building it," he said.

Schneider told a reporter later that he fears the road will be opened to general traffic during rush hors, generating a greater flow of vehicles into and out of the city.

Schneider's comments on Capitol Hill came in response to questions by subcommittee chairman Patrick J. Leahy (D-Vt).

The highway project, approved by former U.S. Transportation Secretary William T. Coleman Jr. in January and reaffirmed in February by his Carter administration successor, Brock Adams, would bar heavy trucks at all times.

Schneider said after the hearing that the car pool and bus plan, to which Virginia highway authorities agreed as a condition for federal approval of I-66, was based on "unsubstantiated conjecture."

He said the plan was base on comparisons with Shirley Highway (I-95). Unlike the I-66 corridor, I-95 is "a heavily traveled bus corridor . . . and after Metrorail gets built to Springfield, you won't even have that much bus traffic on Shirley Highway," Schneider said.

Schneider also said the Shirley Highway bus-car pool plan is relatively successful because in addition to preferential lanes there is preferential parking, especially at the Pentagon, for many commuters.

Schneider said he felt undersue of car pool and bus lanes would create "tremendous pressure" to allow general traffic to use I-66.

"Frankly, I think that's what the strategy is," he said.

The use of the highway by regular traffic, Schneider said would increase traffic and parking problems in the District.

Rather than build I-66, Schneider suggested state highway funds should be used to provide parking for or feeder roads to the Metrorail line also planned in the I-66 corridor.

W.S.G. Britton, deputy chief of the Virginia highway departmen, said in a telephone interview that an environmental impact statement prepared for the state envisions no great impact on Washington traffic when the highway is completed. He also denied that Virginia plans to expand the highway to general use.

At the Senate hearing, Schneider also chided the federal government for doing too little to encourage mass transit ridership, and cited continued subsidization of parking spaces for federal employees as an example.