Virginia Gov. Charles S. Robb yesterday named two Northern Virginians, both major contributors to his campaign last year, to the State Highway Commission, giving the region unprecedented representation on the powerful board.

Robb nominated Alexandria beer distributor Joseph M. Guiffre to represent Northern Virginia on the 10-member panel and Fairfax banker T. Eugene Smith to be the commission's at-large urban member. Tidewater Virginia had previously claimed the at-large seat, and Northern Virginians had hoped Robb would increase their influence by appointing someone from the Washington area to the post.

Robb also announced that he will nominate Robert Smalley, a box manufacturer from Berryville, to represent the western Staunton District.

The three nominees, if confirmed by the General Assembly as expected, will replace commissioners who resigned last year because of alleged conflicts of interest between their highway duties and their private business affairs. The three resignations of Republican-appointed commissioners became an issue in the gubernatorial campaign and gave Robb an unusual opportunity to shape the commission, which awards millions of dollars of contracts each year while deciding where highways will be built.

Guiffre and his company contributed more than $3,300 to Robb's campaign last year and his wife gave another $500, according to state campaign records. Smith, a vice president of the First and Merchants National Bank, and Smalley, president of the Smalley Package Co., each donated at least $1,000, the records show.

Guiffre has supported conservative candidates of both parties, however, and his nomination was welcomed by Fairfax Board of Supervisors Chairman John F. Herrity, a Republican, as warmly as by Guiffre's longtime friend, Democratic Supervisor Joseph Alexander.

"He's a very able guy, and I'm pleased he got the appointment," Herrity said. "The only liability is, he's not a resident of Fairfax County . . . But his major economic interests are here, so that balances it out."

Guiffre was an unsuccessful candidate for state delegate in 1979. He will succeed William B. Wrench, who resigned in September after it was disclosed he had voted to locate the proposed Springfield Bypass highway near property he owns.

"I'm hoping to bring just good business judgment to the job," Guiffre said. "I don't have any preconceived notions. . . I haven't even figured out what the Springfield Bypass is all about."

Smith is a former chairman of the Fairfax Planning Commission and a current member of the Board of Zoning Appeals. He will replace T. Ray Hassell III of Chesapeake, who became the first urban representative in 1974 and resigned last year for what then-Gov. John N. Dalton called "technical violations" of the conflict-of-interest law.

Northern Virginians have long complained that their interests were ignored by the mostly rural highway commission, and they lobbied hard for Robb to appoint one of their own to the at-large spot.