In the days before aquaculture and carotene pigments, before fishermen wrote petitions for regulatory clearances, trout was trout and salmon was salmon. That was all there was to it.

But for the Food and Drug Administration and Van Brown's Carolina Mountain fish hatchery in North Carolina, which have been locked in battle for nearly two years, things are no longer so simple.

In 1988, in the interest of ending consumer confusion about the fish they buy, the FDA ruled that the species Salmo gairdneri must hitherto be sold only under the name "Steelhead Trout." Brown, who raises a million and a half pounds of gairdneri every year, demurred. He mixes a natural red dye into the food he feeds his fish, turning their flesh from a trout-like white to an altogether more appealing, salmon-like pink.

The name Steelhead Trout, he said, does not do his product justice. He wants the FDA to let him call his fish "Salmon Trout."

At stake is more than the label Brown puts on his fish wrappers. North Carolina is a state very much interested in making a big business out of aquaculture, seen as a lucrative alternative to the troubled tobacco industry. And officials are aware of how much bigger that business would be if steelhead trout could become salmon. Brown estimated, for example, that just including the word "salmon" in his product's name would allow him to fetch an additional 50 to 75 cents a pound.

This has brought the political heavyweights into the fray. North Carolina Gov. James G. Martin (R) has made a direct appeal to the FDA, as have Sen. Jesse Helms (R-N.C.) and Rep. J. Alex McMillan (R-N.C.), who buttonholed FDA acting commissioner James Benson for two hours this week when the agency chief made his weekly rounds on Capitol Hill.

At the same time, the economic consequences of Brown's proposal have not been lost on the states of the American Northwest, which sell several billion dollars worth of salmon every year in supermarkets and are not about to let their market monopoly be usurped by what they see as regulatory sleight of hand. Just after Helms weighed in, Sen. Bob Packwood (R-Ore.) sent a letter and the Western salmon lobby began to raise a ruckus.

"You can't call anything that comes out of the ocean red snapper," said Tom Robinson, administrator of the Oregon Salmon Commission. "So why should you be able to call something salmon that isn't one of the five known salmon species?"

If the dispute were only about money and market share, however, it might be simple. But it is not.

Just a year after the FDA required all Salmo gairdneri be sold as steelhead, the American Fisheries Society (AFS), which is the bible on such matters, made an important announcement. Based on new data from scientists at the University of Michigan and a comparison with species caught off the Soviet peninsula of Kamchatka, the society said, Salmo gairdneri was more properly classified as Oncorhynchus mykiss, which, in layman's terms, is the category to which Western salmon belong.

"We still call a {steelhead} a trout because of longstanding convention," said Robert Kendall, an AFS official. "But the steelhead trout is actually more closely related to Pacific salmon than it is to the true trouts, the brown trouts of Europe."

Brown's hatchery-grown North Carolina trout, in other words, are salmon.

What remains is best described as a regulatory mess. FDA officials have not yet decided which way they will rule. But it's clear the agency is not obliged to heed the latest scientific classifications of fish species, but only to ensure that fish names are not confusing to the public.

On that score, even the American Fisheries Society favors holding on to the traditional term, steelhead trout.

"The society has been working for 50 years to standardize the vernacular names of fish," Kendall said. "These common names are much more stable than the Latin scientific names. People have known this as the steelhead trout and we'd rather stick with that name."

On the other hand, what Brown wants to sell clearly is not ordinary trout, because of its color and because of the steelhead's new classification. In talks this week with Brown, FDA officials appear to have been sensitive to this position and are considering several possible compromises.

One is to call the fish Salmo trout, which gives Brown the suggestion of salmon without quite spelling it out. Others favor a less oblique solution.

"If they're not breeding any new kind of trout and there's not anything different about it, I would think that 'artificially colored trout' is the best description," said Charles Mitchell, an attorney with the Center for Science in the Public Interest, an FDA watchdog group.