Alexandria lawyer James M. Thomson, once the most powerful Northern Virginian in the House of Delegates, has been selected to head the state's insurance regulatory agency, the chairman of the State Corporation Commission said over the weekend.

SCC Chairman Junie Bradshaw said he hoped Thomson, a key Democratic figure for 22 years in the House before his highly controversial election defeat in 1977, would assume the $48,000-a-year position in time for the start of the General Assembly's January session.

Thomson, the House's majority leader at the time of his defeat, has pursued a private law practice in Alexandria since leaving Virginia politics. He was engulfed in controversy again two years ago when he failed to win the backing of the Alexandria bar in an unsuccessful bid for a state judgeship.

Black and women opponents complained at the time that Thomson was insensitive to the interests of minorities -- criticisms that also dogged his last campaign for the House.

Bradshaw praised Thomson Saturday, saying the SCC's three commissioners had selected him unanimously because they wanted "a bright legal mind who would be fair and interested" to head the insurance division, the SCC's largest with about 100 employes.

Bradshaw also said he expected Thomson, a Democrat, would generate good relations between the agency and the Democrat-dominated General Assembly, which considers the agency's legislative program each year.

Thomson refused to comment on his selection and was sharply critical of disclosure of his appointment by The Alexandria Gazette. "After 22 years in politics serving Northern Virginia, The Gazette wrote nothing but negatives," Thomson said. "You're going to do the same thing, so you write your own story and don't bother me anymore."

Bradshaw said the possibility of Thomson's appointment arose recently "when Jim was sitting in my office one day and I suggested he get back into the role of serving the Commonwealth." Thomson, a popular figure with many state legislators, still owns a home in Richmond's Fan district.

Thomson was in line to become chairman of the influential House Appropriations Committee when he was upset four years ago by Alexandria Republican Gary Myers after a bitter campaign that focused on Thomson's staunch opposition to the Equal Rights Amendment and his record on racial issues.

Those issues surfaced again in 1979 when Thomson sought support among Alexandria legislators and lawyers in a bid for a vacant circuit court judgeship. In a rare slap at a longtime legislative leader, Thomson's opponent for the bench, Alexandria lawyer Albert H. Grenadier, won the post.

Some House Democrats suggested at the time that Thomson might be a popular candidate for the State Corporation Commission or the Virginia Supreme Court at a later date.

The position of insurance commissioner was left vacant earlier this month by the resignation of Jay Newman, who returned to the private insurance industry.