Virginia Democratic candidate for governor Gerald L. Baliles sharpened his attacks yesterday on his Republican opponent, Wyatt B. Durrette, charging in a debate in Reston that Durrette had changed his positions on several key issues.

Durrette, although he acknowledged last week that he had changed some of his views for the better, yesterday labeled Baliles' accusations "distortions" and fired salvos of his own at Baliles for altering his opinions and for supporting expensive social programs.

Durrette said afterward that he was confident that he had performed well, but he frequently seemed on the defensive as Baliles hammered away at his changed positions as well as his stand on state aid to education and other issues.

"He has adopted Peter, Paul and Mary's theme song of a decade ago, 'Blowing in the Wind,' " said Baliles. "He has changed his course. He has repudiated his direction." Baliles charged that Durrette is "more interested in tailoring opinion to shape a campaign than to adhering to principles and to conscience."

Forced to defend himself repeatedly, Durrette said, "My views and my philosophy are well known to the people of Northern Virginia. They are the same today as they have been for 10 years." Durrette, who lost to Baliles in a 1981 race for attorney general, is a former state legislator from Fairfax County.

The debate, held before nearly 400 business leaders and politicians in Reston, was one of the sharpest clashes between the two men in the campaign, their campaign aides agreed.

Durrette, a Richmond lawyer, stressed his ties to Northern Virginia and his support of transportation issues, such as continued state funding for Metrorail and expediting design of the Springfield Bypass and the proposed commuter rail system.

Baliles, who served as a state delegate from the Richmond suburbs and as state attorney general until last month, endorsed those steps, as well as state help in widening Rte. 28, a major development corridor in western Fairfax, Prince William and Loudoun counties.

Durrette strongly supported the "tax simplification" proposal advanced by President Reagan, and he said the president's package "will make very little difference" in the amount most families will have to pay in taxes. He said Virginians should back the administration's proposal "for the greater good of the nation," and he chided Baliles for favoring further study of the effects of the tax plan.

Perhaps Durrette's strongest criticism of Baliles came in an exchange on social spending. After Baliles declared that families on welfare were "entitled to the basic necessities of life" and backed more funding for social programs, Durrette declared that the Democrat "fails to recognize 20 to 30 years of history" that proves increased funding is "not a solution to the problem."

Durrette called for a subminimum wage to help create jobs for the unemployed and slammed Democrats in the House of Representatives for opposing that legislation.

On education, Baliles said he was "amazed" that Durrette had declined in a debate last week to endorse a proposed $500 million increase in school spending during the next two years. The proposal is part of the budget being drafted by Gov. Charles S. Robb, who cannot succeed himself.

Durrette replied that he was committed to improving the quality of education, but he expressed doubts that the funding would have that effect. He said he favors merit pay and continuing education for teachers and upgrading textbooks.

The debate strayed into foreign policy when the two candidates were asked if they would allow the Virginia Power Co. to buy coal from South Africa.

Durrette said he favors buying coal from the cheapest source and added that "the form of slavery in Poland is more obnoxious to me than that of South Africa" because Poland "exports tyranny."

Baliles said he would not tell Virginia Power where to buy coal.