It would be premature to say the bluefin tuna has completed its comeback, but things are at least looking up for this compact, fast-swimming gamefish that grows to over half a ton.

During the second week of June fishermen off the southeast Virginia coast scored heavily on schools of the iridescent blue-green fish. Carry T. Holland returned to Rudee Inlet with 13 bluefins one day, 11 the next. Mike Harrison of Virginia Beach caught a 151-pounder from Captain Andy Morris' "Putt-Putt" with a slow-trolled spoon, the largest bluefin taken since the state-record fish of 204 pounds in 1977.

Since that first flurry things have gotten even better. At last report boats out of Wachapreague and Virginia Beach were averaging 20 tuna. Last year President Carter and family boated an all-too-typical three fish in a long day.

Such increased catches of young tuna show the bluefin is at least holding its own against overexploitation by commercial fishermen, and perhaps gaining a little.

It's a good thing. Some consider the bluefin almost an endangered species. Fred Rushin of the Cape Henry Billfish Club frets over tuna stocks like a hen over her chicks. "Tuna stocks have dropped drastically in recent years," he said, "hence the need for management programs and laws to protect and rebuild the stocks." Five years ago, he said, a good day's fishing meant 40 or 50 bluefins. Last year seven to 10 tuna was considered excellent.

Rushing does more than just worry about tuna. In cooperation with a study by the Wood's Hole Oceanographic Institution in Massachusetts, he tags, releases and reports virtually all the bluefins caught from the private boats he skippers.

"I started in 1969 and have probably tagged somewhere around 200 tunas from six to 135 pounds," says Rushin, a wisp of a man. "We don't really know how bad off they are. There's a lot we don't know.

It is known is that tuna stocks have declined drastically over the last two decades. Particularly hard-hit are the 5-to 8-year-old class, 115 to 300 pounds. These medium-sized fish are the big breeders.

Before 1958, bluefin tuna stocks were fairly stable and only lightly exploited. The introduction of purse-seine fishing that year almost sounded the bluefin's death knell.

By the time seining peaked in 1963, the dreadfully efficient technique had decimated whole age classes, especially the breeders. The commercial take of Atlantic bluefin dropped from 38,500 to 12,500 metric tons between 1964 and 1973.

In 1973 F.J. Mather III told the 16th Annual International Game Fish Conference that catches of large bluefin had declined "catastrophically," tag return rates were alarming, and there was a dangerous imbalance in the age groups.

In 1967, before the full effects of purse seining had been felt, 1- and 2-year-old tuna comprised only 30 percent of the population; in 1975, they represented 61 percent. Bluefins over 13 years old were 2 percent of the population in 1967, 19 percent in 1975.

Al Ristori of the Emergency Committee to Save America's Marine Resources and the Mid-Atlantic Fisheries Management Council feels that tuna aren't endangered, but are "seriously overfished. Heavy U.S. and Canadian seining in the '60s . . . virtually eliminated entire year classes."

He said the big problem is that "elimination of tuna from the 200-mile law prevents us from controlling the foreign catch."

U.S. regulations limit sport anglers to four fish per day, only one of which may be over 115 pounds or under 14 pounds. The program, begun in 1973, also places some restrictions on commercial catches.

It seems to be working. The 1973 year class is strong. Ristori says this class "can save tuna fishing if it's preserved."

Tighter controls on the commercial catch are needed, however, as well as a greater emphasis among sport fishermen on tagging and releasing fish. For information on applications for tuna tags, write Bluefin Tagging, 75 Virginia Beach Drive, Miami 33149.

Bluefins are believed to move up the East Coast in three "waves." First come the "giants" that travel early, deep and far offshore. No sportfishing is done for these old, elusive fish off the Mid-Atlantic coast.

The second wave consists of the small fish, generally 2- to 4-year-olds of 20 to 100 pounds, which make up most of the sportfishing catch in the Mid-Atlantic. Depending on the weather, they stay anywhere from three to eight weeks, till mid or late July.

The third group is the medium-sized fish; the few from this depleted class that are captured usually come in late July.

The Southeast Lumps, roughly 25 miles offshore, produced the earliest tuna this year, but catches have also been made at the Fishhook and the Hotdog. Some of the heaviest concentrations have been found by Wachapreague skippers at 21 Mile Hill.

Bluefin tuna are among the strongest of offshore gamefish. Built like a football, they are dense, compact fish that fight with devilishly forceful runs and heavy plunging. Most of the tuna are schoolies of 20 to 40 pounds, but on light trolling outfits with no weight they put up a battle.

When you've mastered one and worked him to the baot, think hard before letting the mate sink the gaff. "At this stage, every fish counts," Rushin says.

Tuna trips can be arranged through the Virginia Beach Fishing Centre at Rudee Inlet (804/422-5700). Charter fees run $273 for a party of six, $55 per person for makeup parties. At Wachapreague, charters for six run $205. Phone 804/787-2015 to set up a trip. CAPTION: Picture, DONNY LIVERMAN RELEASES BLUEFIN TUNA TAGGED FOR POPULATION RESEARCH. Photo by Gerald Almy.