Del. Richard R. G. Hobson (D-Alexandria) formally endorsed attorney Albert H. Grenadier yesterday for an upcoming Alexandria Circuit Court judgeship, the third major endorsement Grenadier has received in the last five days.

The Alexandria Bar Association and a citizens' advisory panel convened by Hobson last week also picked Grenadier over James M. Thomson, former majority leader of the Virginia House of Delegates.

Thomson's campaign to replace Judge Franklin P. Backus, who will retire on Feb. 1, has been opposed by some younger Alexandria lawyers and by local feminists and civil rights groups.

In a statement yesterday. Hobson, the senior delegate from Alexandria said, "Mr. Grenadier's professional qualifications and community support demonstrate that his election as a judge will not only promote the efficient and fair adminstration of the judicial system, but also will be perceived as such by the citizens of the city."

Del. Elise B. Heinz (D-Alexandria/Arlington) has previously announced that she would support Grenadier in view of his bar association endorsement.

Thomson last week said he was considering seeking the judgeship without the backing of the local bar association, an unusual procedure in Virginia where legislators usually elect judges who have been endorsed by local law groups. Thomson could not be reached yesterday for comment.