The seafood market at the City Dock here still sells rockfish, the traditional premier sport and table fish of the Chesapeake Bay, but it's no pleasure to buy anymore.

At times this year $10 bought a single fish the salesman could pick up with two fingers. The price went as high as $4.99 a pound.

A veteran waterman from Rock Hall recalls that not too many years ago a 20-foot skiffload of rockfish (called striped bass everywhere but the Chesapeake) drew $150 at the dock. "Now," he says, "a bushel basketful is a $100 bill."

Times change fast. Just 10 years ago the Chesapeake bulged with rockfish. The men who work the bay caught more stripers in 1973 than they had since records were kept, and sold them for as little as 25 cents a pound. That year, the Maryland Department of Natural Resources estimated, just shy of 5 million pounds of the striped delicacies came to market.

Countless more tons were captured by sport fishermen, who concede today, in the words of one, "We made pigs of ourselves."

It was a bonanza that commercial and recreational fishermen and people who enjoy good food all delightedly took for granted.

Then, suddenly, the bonanza ended.

Last year the commercial rockfish catch in Maryland totaled 400,000 pounds, the lowest since 1933 and less than 10 percent of what it was in 1973. Officials believe that the catch actually might be the worst ever, the 1933 tally being based on suspect figures.

All but a handful of sport fishermen gave up pursuing rockfish in favor of the more plentiful bluefish and sea trout.

Said DNR biologist Harley Speir, pointing to a chart depicting a decade of precipitous decline for Maryland's designated state fish, "Horrifying, ain't it?"

Speir and his colleagues believe that the collapse of rockfish stocks in the bay has one cause: poor reproduction, due partly to climate, partly to the natural ebb and flow of fish populations and partly to pollution.

Rockfish hatch in the fresh or brackish water of the bay's tributaries, including the Potomac, and grow up in the estuary. The females spend much of their adult lives cruising the coastal Atlantic but return each spring to spawn in the rivers where they began life. The Chesapeake, with miles and miles of spawning habitat, is thought to be delivery room and nursery for most of the rockfish on the East Coast.

Lately when they returned, roe-heavy stripers found no reproductive Shangri-La. For the past eight years spawning success in the Chesapeake ranged from below average to awful. In 1970 it was spectacularly good. In 1981 it was the worst in the 30 years the DNR has been checking.

Scientists think that industrial and farming pollution and urbanization along the rivers combined with imperfect weather to create a spawning disaster. Everyone worries. Even the federal government jumped in with a three-year emergency study to determine the cause of the decline, on grounds that it affects fishermen from Maine to North Carolina.

Tests by various agencies showed that heavy metals and industrial PCBs, agricultural pesticides and chlorine from sewage treatment plants all can damage spawning success when introduced into test waters in amounts similar to those found in the rivers.

Diabolically, the weather hasn't been good, either. Good spawning years tend to follow winters where there is an early freeze, locking detritus up the rivers and marshes, followed by flooding or high flow in the spring, which brings the detritus roaring downstream with a wealth of nutrients, creating a groaning board of organisms for the just-hatched fry to feed upon.

That hasn't happened lately.

Even the nursery grounds for young stripers--weed-choked backwaters where tiny fish hide and feed off the grasses--have been decimated. Many were scoured clean by Hurricane Agnes in 1972 and much of the grass never returned.

It adds up to a miserable circumstance, but not one without hope.

Last year the DNR's seine surveys of spawning areas turned up evidence of only slightly below-average reproduction, the first decent spawn in three years. Commercial fishermen have found good supplies of young, undersized fish in their nets this winter, which they returned to the water.

The decline has brought commercial and sport fishermen and DNR officials to a rare, fragile consensus. They worked together on rockfish conservation schemes. Larry Simns, head of the Maryland Waterman's Association, which long has quarreled with DNR, says now that the state agency is "doing everything they can" to protect remaining stocks and improve spawning habitat.

Privately, some commercial and sport fishermen even whisper about giving up striper fishing altogether for a few years, in hopes the species will rebound if left alone.

Watermen have accepted DNR limits that ban all fishing in spawning areas in the spring and in the mid-bay all summer long; charter and sport fishermen are limited to catches of no more than 10 rockfish per day per person.

Watermen and the DNR are operating hatcheries where rockfish eggs are "milked" from pregnant females and fertilized. The resulting fry are introduced into rivers to augment the natural hatch.

State and federal officials are seeking to restore and protect striper spawning habitat through enforcement of the Wetlands Act and the Clean Water Act, flood plain regulation and the reduction of chlorinated discharge from sewage treatment plants.

Meanwhile, the pursuers of stripers grow fewer and fewer. Veteran commercial fishermen guess that perhaps 15 watermen are now supplying 90 percent of the Chesapeake stripers brought to market, where once hundreds set net. In the warm months the once-burgeoning sport of rockfishing is practiced by only a few diehards.

The trade in stripers is down to a trickle at the seafood markets.

Who would pay almost $5 a pound for a fish that 10 years ago was commonly given away?

"Just 'torsts,' I guess" said a woman at an Annapolis seafood house, using the Baltimore word for tourist. "Torsts will buy anything."