Legendary restaurateur Duke Zeibert may be back in business next spring at his former location at the corner of Connecticut Avenue and L Street.

"It's 90 percent certain," Zeibert said 21/2 weeks ago about plans to open a 350-seat restaurant on the mezzanine level of the new Washington Square complex.

Why would the 70-year-old Duke want to get back in the business?

"All I do now is play golf, play bridge and go to the race track," says Zeibert, "and there's aggravation in all three. But there's no aggravation like the restaurant business. You miss that kind of aggravation. Plus, I got my son Randy, and I want to keep the name going. Randy has sons, and restaurants go on generation after generation. I've been on the Pritikin diet for three years, and I've got the body and stamina of a 50- year-old man."

One major addition to the restaurant landscape since Zeibert's retirement several years ago is Mel Krupin's, owned by and named after Zeibert's former maitre d'. Krupin took over nearby Paul Young's, instituted a menu similar to Zeibert's and captured much of Zeibert's clientele.

"There's nothing wrong with Mel -- he's a nice boy," says Zeibert, who anticipates as pleasant a relationship with Krupin as he had with Paul Young before him.

Footnote: Zeibert recently returned from Atlantic City where he turned down an offer from the Golden Nugget hotel and casino to lend his name to a swanky steak house. Says Zeibert: "Washington is my home.