Virginia Democratic Gov. Charles S. Robb, in some of his sharpest political statements this year, today strongly backed state Sen. L. Douglas Wilder's campaign for lieutenant governor and derisively questioned the credibility of Wyatt B. Durrette, the Republican candidate for governor.

Robb said Wilder "is clearly in the mainstream" of moderate Virginia politics and is a respected member of the Senate, where much of his record is "almost identical" to positions supported by Durrette when Durrette was a legislator from Fairfax County in the early '70s.

But Robb, echoing a theme used by Democratic gubernatorial candidate Gerald L. Baliles, said Durrette, unlike Wilder, has switched positions on several issues.

Durrette "of course, has the right to change his mind as often as he likes," said Robb, who under Virginia law cannot succeed himself.

Robb's comments revived a political spat that started last May when Durrette called Wilder "the most liberal" candidate ever to seek the number two spot.

Wilder challenged Durrette to justify the charge, suggesting some might interpret "liberal" as a code word for racism. Wilder is black.

Durrette denied the assertion was racist and cited a conservative Northern Virginia group's rating of the legislature as the basis for the label. Those ratings have been disputed by Wilder.

Robb said of about 20 issues he reviewed, Durrette and Wilder disagreed on "only one or two."

Although Robb did not specify them, Durrette repeatedly has defended himself for no longer supporting such issues as the Equal Rights Amendment and so-called "meet and confer" bills that would allow government employes a limited right to negotiate better working conditions. Wilder supports both.

"In fact the kind of soft spots Republicans describe . . . are not there," Robb said of Wilder's record.

Robb said he was uncertain whether the issue of Wilder's race in this largely conservative state would have much of an effect in the Nov. 5 election, in which Wilder faces state Sen. John H. Chichester of Fredericksburg, the GOP nominee.

He said he doubted that Republicans "as a matter of pure politics" would try to exploit it. "They don't need to remind anyone . . . that point already has been well made," he said of media reports about Wilder.

Robb also dismissed criticism from Durrette of his prison and parole policies as "inaccurate" and said those issues lend themselves "to campaign rhetoric." Durrette has charged that Robb's administration has been too lenient on paroles and is keeping state inmates in local jails to ease pressure on the state's troubled prison system.

On paroles, Robb noted, as Baliles did last week, that Durrette, now a Richmond lawyer, once supported a more liberal parole policy. "He was advocating . . . even more permissive" legislation, Robb said.

Don Harrison, Durrette's press secretary, today said Durrette's "views on the major issues have been consistent for the past decade or more."

Harrison noted that both Republican and Democratic sheriffs this week complained of overcrowding in their jails. He said prison and parole problems have changed in the past decade. "We are offering practical solutions," Harrison said.