By Paul Reidinger

AMONG MODERN MARVELS , supermarket sushi occupies a special place at the intersection of convenience and dread. You can pick up a tray on your way home from work and feel virtuous and sophisticated, and at the same time you can't help but wonder if, come 4 a.m., you will regret having actually eaten it for dinner. Who prepared it, after all, and how long was it sitting there, adequately or inadequately chilled, before you snapped it up and got your club-card discount?

Life in a sense is a long series of these kinds of cost-benefit analyses, but supermarket sushi signifies even beyond that. It tells us that sushi has entered the mainstream of American food culture (though it's still wading in the shallows near shore), and it prepares us not to be surprised when sushi, as a restaurant food, starts turning up in various unlikely places, from the Voodoo Lounge to M Point, the late-'90s spot in the Hotel Milano, where it balanced a California-cuisine menu.

In true American fashion, we have seized sushi and now, through wild and rash experiments, are trying to figure out what can and cannot be done with it, how we can make it our own. Given that the sine qua non of American food is the hamburger, we can perhaps forgive ourselves for wondering if sushi's final destination on these shores might be McDonald's – McSushi, with McSake in collectible plastic glasses. While we await this interesting development, we can sate ourselves with a visit or two to Blue Fin Sushi, a newish Richmond District spot that is also the Siamese twin of a sports bar called Prime Time.

It is possible, within these curious walls, to open with some hamachi nigiri ($4.25 for two pieces) before moving on to a burger – a Ball Park burger ($6.95), say, with Jack cheese, lettuce, tomato, pickles, and excellent crispy-creamy fries. But it is possible only within the Prime Time side of the layout, where each of the half dozen or so TV screens, mounted high on the wall to aid viewing, is tuned to a different channel. (We saw a live worm-eating contest and had to rearrange ourselves so we would be looking at something slightly less appetite-killing, like hockey brawls.) Sushi and other (cooked) Japanese dishes move from the Blue Fin kitchen the few steps to the sports bar, but that traffic is one-way; the sports bar's food, though excellent of its kind, does not move into the snazzier precincts of Blue Fin.

The restaurant's real eye-catcher is, mounted over the sushi bar, a huge fish with an immense, ruffled blue dorsal fin and a marlin- or swordfish-like lance extending from its face. Bluefin is a type of tuna, and tuna in its various guises is important material for sushi chefs, but this fish is not any kind of tuna. On the other hand it is spectacular, and the sport-fishing spectacle of it does have a way of keeping the restaurant's name (and namesake) fresh in the mind.

Tuna – "chicken of the sea," as the old TV commercial so cleverly reminded us – takes well to spiciness, and Blue Fin's chefs aren't shy about furnishing the latter. The "special spicy sauce" in the volcano salad ($8.50) – a reddish orange flow with the consistency of ketchup – set our mouths quietly on fire and almost, though not quite, overwhelmed the meaty coolness of the cubed fish. Cubes of avocado (also cooling, rich) helped keep the peace, while the tangle of fried rice-stick noodles provided some visual interest and a distinct chopstick challenge.

Perhaps because of the nearby sports-bar vibe, Blue Fin's menu is quite rich in cooked and innovative items. There is plenty of nigiri and sashimi, of course, along with more than 30 rolls, among them the restaurant's signature Prime Time maki ($8.50), a nesting of salmon, eel, and avocado in mame nori – soybean paper of a pale pink hue, like the petals of an early-spring rose. But the cooked stuff is irresistible, from mushroom stuffy ($5.95) – an oysters Rockefeller-like trio of shiitake mushroom caps packed with snow crab meat and baked with a spicy cream sauce – to a simple tail of baby lobster ($6.95), grilled and served with mango salsa. Lobster so often is drowned in butter (a formidable if subtle flavor in its own right), but here the spareness of the treatment lets the shellfish speak in its own voice. The heavier spicing is reserved for items that benefit by it, such as slices of duck breast ($9.95), marinated in five-spice paste and served with an unexpected, rubbery-crunchy mélange of sautéed shiitake slices and halved pistachio nuts.

On the other side of the host's station, of course – at Prime Time – most everything is cooked, the exceptions being the salads, such as the Olympic Track ($6.45 for a full-size, splittable version). The name is vaguely Hellene, and the salad – a wealth of baby lettuces, red onions, olives, mushrooms, and artichoke hearts – does resemble what most of us know as Greek salad. The differences are a lack of tomatoes and the presence of grated mozzarella cheese instead of the saltier and more pungent feta; these changes are muting.

Cooked items are handled with skill. Fried calamari ($6.95) was tender within delicate golden crusts, while a spicy-chicken pizza ($6.45) needed just a bit of salt to release its exotic perfumes: the chicken had been marinated in a ginger-peanut sauce, tomatoes gave way to cilantro pesto, and the cheese was fontina, dotted with scallion rounds. And that is all, the end, no more, or, as they say in Spanish, fin. Blue Fin Sushi/Prime Time. 1814 Clement (at 19th Ave.), S.F. (415) 387-2441. Daily, 5-11 p.m. Beer and wine. MasterCard, Visa. Moderately noisy. Wheelchair accessible.