When Virginia Gov. Charles S. Robb was asked a while back to justify his speechmaking travels, he explained that he was putting the Old Dominion back into the national political spotlight. Never mind that it wouldn't harm Robb's own presumed ambitions for higher office, perhaps a shot at the Democratic vice presidential nomination.

Now comes word that the Texas election, the defeat of that state's Republican Gov. William P. Clements Jr. for a second term, may soon push Virginia and Robb into a position of higher visibility -- and at a strategic time for jockeying for the 1984 elections.

Last July, Clements became chairman of the Southern Governors Association and Robb its vice chairman. In the normal course, probably next July, Robb would have succeeded Clements.

But with Clements' defeat, the first of a sitting chairman in the association's history, the question of filling the top office in the interim has been tossed to a special advisory committee that meets next week in Florida. Current by-laws are silent about such situations.

One prospect is for Robb to take over as acting chairman until July, then to become full chairman, giving him a lock on the office's prestige until the time of the 1984 party conventions. (The group will move its headquarters in January from Atlanta to Washington.)

What does Robb think? Ever discreet, he thinks a premature comment would be inappropriate, an aide said.