Open Monday through Friday 11:30 a.m. to 11 p.m.; Saturday 6 to 11 p.m. AE, CB, D, MC, V. Reservations. Prices: Lunch main courses $4 to $9; dinner main courses $9.50 to $17. Dinner with wine, tax and tip averages $25 to $30 a person.

Abbott and Costello couldn't have carried it off; Abbott was too thin. The Marx brothers would have spoiled the ambience with cigar smoke. Joe and Mo's only problem as a comedy team of restauranteurs is that neither one of them acts the straight man. That is left to you, the diner.

Joe and Mo are the ambience. Both look as if they know and love food -- presumably good food. They describe theirs to you in a way that makes you believe that the roast beef is not only going to be wonderful, but it will make your life more fun and improve your repartee as well. Whatever personality the dining room lacks -- and it is remarkable how the old blue velvet and tapestried luxury of Nathan's II was so subtly turned into a mishash of tiles and carpets that look like remnants against the factory-blue-gray walls -- is compensated by the human beings one encounters. The waiters, in gray cotton jackets that waiters affect in top-priced steak houses, act like pals, inside tipsters. They are young and brash and intent on keeping your coffee cup full. They leave the impression that if there is anything you need -- from a fork to the winner of the third race at Bowie -- they will have it for you nearly before you request it.

The menu is simple steakhouse food, the kind you hope to find throughout America but rarely do. There are sirloin, porterhouse, filet and prime rib, several fresh fish steaks, a couple of veal scallops, duck and individual rack of lamb. The first promising sign is that there is no surf and turf on the menu. If the format looks similar to the Palm, the comparison is an honest one, since Joe and Mo came from the Palm training ground.

Bring a voracious appetite. Not only are portions enormous (three big slabs of meat loaf at lunch, for example), but Joe and Mo have managed to find bread of stellar character, raisin pumpernickel and onion rye with guts. The is the place to eat old-fashioned, straightforward meat-and-potatoes meals after a hard day of felling redwoods.

You could start with snails in mushroom caps -- very earthy and fragrant from the well-browned mushrooms -- or green noodles with cream, ham and cheese -- nicely done but not memorable. A cold marinated seafood appetizer was overcooked and underseasoned; oysters or clams on the half shell are probably a better choice. But the most satisfying appetizer is likely to be soup, a thick cream of vegetable or tomato with depth.

Main dishes are the stars here. After long seeking roast beef that had more to boast than tenderness, I wanted to pin a blue ribbon on Joe and Mo's. It cost $12.50, was served in a thick slab without bone (because aging ruins the bone, we were told) and slightly overcooked but nevertheless juicy and permeated with its seasonings, dominated by rosemary. The vital point was, though, that it had the flavor of real beef, aged beef, beef bred on good feed. Blue ribbon stuff. The sirloin also, a full boneless pound for $15, was well-aged and full-flavored, cooked as rare as we wanted it and totally satisfying, though a hotter fire would have seared the surface better. An order of bordelaise sauce to accompany it served only to warn others that it was best avoided. The beef is matched by the fish steaks; deeply pink salmon ($11.50) was sliced thick and broiled perfectly so the surface was crisp edged and the interior juicy. The swordfish steak was every bit as fresh, but overcooking had turned its flesh chewy. I would try it again, warning the waiter that overcooking such fine fish ought to be considered a criminal act.

I never got around to the rockfish, red snapper or sole. The shrimp, in a creamy herbed sauce described by one companion as "blunt," is apparently being taken off the menu. Veal is as high class as the other ingredients, and one day's special was a veal chop a full two inches thick, but it had been distractingly stuffed with crabmeat that would have fared better on its own. The most obvious flaw in Joe and Mo's kitchen is a tendency towards gimmickry; an otherwise grand individual rack of lamb was topped by a thick, pasty "stuffing" that reeked of uncooked garlic and did nothing for the lamb but insulate it. Joe and Mo's has the makings of a monument to good plain food, and has no necessity for invention.

At lunch the sirloin drops to$9, the fish steaks to $7, and a few chicken, veal, cold dishes and omelets flesh out the menu. If, along with the perfect roast beef you have been seeking a stunning chef salad, you'll have to add lunch at Joe and Mo's to your schedule. A plate is piled high with quadrants of fresh-cooked turkey, freshly roasted beef, ham and swiss cheese over romaine with radishes, tomato wedges and olives. The creamy dressing could use a spark or two, but the chef can be proud. Daily specials are homey, with meatloaf a favorite, particularly because it comes with real mashed potatoes (you can tell by the honest-to-goodness lumps, in case you no longer remember real potatoes) -- are rare as good pumpernickel.

Steak and seafood choices are the easy part. The hard decisions are the vegetables. You must, of course, order potato pancakes. The ones you make at home might be a tad crisper or slightly more lacy, but only if you are a very good cook. Otherwise, it would be a pity to miss them here. Fried onion rings, too, are outstanding, thin and crisp, with the flavor of well-fried onions rather than just fried batter. If you can't choose, order both. You can get a half-portion, which is twice as big as a portion deserves to be anyway. You can skip the other vegetables if our string beans were representative. They tasted like fresh beans left in their cooking water until they became a perfect facsimile of frozen beans.

The wine list is as short and apt for the menu, its prices decent. In light of the crowded bar, this appears to be a beer and booze place more than wine-wise.

Such a meal as one eats at Joe and Mo's is properly ended with a cup of good coffee and a doggie bag, both of which are available. A dish of raspberries might be countenanced, even with a bowl of whipped cream on the side. And people have been known to try the chocolate mousse -- very dark and very good -- or the less-memorable chocolate cream cheese pie. I wouldn't be surprised, though, for somebody to order another round of potato pancakes for dessert.

Joe and Mo are still rehearsing their act. The kitchen can be slow, and some dishes need some rethinking. But the raw material shows talent.