Virginia Sen. John W. Warner vowed yesterday to fight the White House's expected nomination of an aide to Attorney General William French Smith to a federal appeals court in Richmond, branding the aide's qualifications "inadequate."

Warner, the state's senior Republican senator, said his opposition would be "unreserved and unrestricted" if President Reagan names 36-year-old Kenneth W. Starr of McLean, Smith's legal counsel and chief of staff, to a vacancy on the 4th Circuit Court of Appeals instead of one of three federal judges from Virginia he has recommended.

Warner said American Bar Association guidelines on judicial selection and his own experience as a lawyer have convinced him that "There is a certain amount of maturity that is treasured in our judicial system. It is frankly gained only through the school of hard knocks . . . I cannot translate immediately Starr's experience and say it equates to what I consider the standards for a federal circuit court of appeals judge," he said.

Warner's comments marked his strongest public display of opposition so far to Starr, a former partner in Smith's Los Angeles law firm and onetime law clerk to Chief Justice Warren Burger.

The senator said he told Starr after a meeting about six weeks ago that he believed Starr's background was inadequate to meet the ABA's guidelines and criteria "outlined by a very widespread group of Virginians who are knowledgeable on this subject."

The senator's announcement, in a Capitol Hill committee room, sets off a confrontation with the president similiar to one that erupted during the last administration when Sen. Harry F. Byrd Jr. killed Jimmy Carter's nomination of Richmond judge James E. Sheffield to become the first black federal judge in Virginia.

There is an important difference with Warner's opposition. He will be attempting to kill an appeals court nomination and the practice of senatorial courtesy which enabled Byrd to block Sheffield does not automatically apply in such cases.

A Justice Department spokesman said last night it was the department's policy not to discuss the selection process. Starr could not be reached for comment.

Warner said yesterday he had discussed his opposition to Starr recently with White House staff aides Edwin Meese, James Baker and Fred Fielding and with the attorney general, who he said "listened very courteously." Warner said FBI background checks on Starr have begun.

Close examination of Starr's resume, which Warner handed out in a meeting with reporters, "reveals a minimum of experience at the trial level and the appellate level and generally in the practice of law," he added.

Warner has recommended Reagan choose from among District Judges Albert V. Bryan Jr., 56, of Alexandria; J. Calvitt Clarke Jr., 62, of Norfolk, and Glen M. Williams, 62, of Jonesville in Southwest Virginia. Clarke and Williams are Republicans; Bryan is a Democrat.

The senator yesterday released the text of a letter he sent to Reagan Thursday urging the president to pick one of the three for the appeals court seat, which traditionally has been filled by a Virginian. He said he was uncertain whether to speak to Reagan directly.

Warner also said he has met several times recently with Senate Judiciary Chairman Strom Thurmond (R-S.C.) about the nomination, as well as various committee members. He said some of the senators reacted with "frankly some astonishment . . . that a man of this relatively young age and with so few years in active law practice might take on this heavy responsibility."

Warner said that in his meetings with White House staff members, "I strongly detect a divergence of opinion among the principal aides on this issue," but declined to give specifics. He conceded, however, that historically an appeals court nomination is difficult to stop once it reaches the Senate.

Asked if Starr might be considered for a different appellate vacancy, Warner said he knew of none. He acknowledged "some speculation with reference to the Circuit Court of Appeals in the District of Columbia in view of the advanced age of one or more of the members."

If Starr is nominated for the Richmond position, Warner said, "It seems to me it sends a rather strong signal that sitting federal judges don't carry the weight they once did in terms of judicial appointments."