A group of oil companies is abandoning its fourth exploratory oil and gas well in the mid-Atlantic, about 110 miles southeast of Atlantic City, because it was unable to find commercially feasible quantities of oil and gas after drilling for more than a year at world-record water depths.

Shell Offshore Inc. and its partners, which have spent about $400 million drilling for oil off the Atlantic outer continental shelf, are capping a final exploratory well 79 miles east of Chincoteague, Va.

The three companies bought the lease for the well in 1981 and have spent about $27 million drilling for oil in water more than 5,000 feet deep off the Virginia coast since July 12.

"We are in the process of our plugging and abandoning procedure," said Jimmy Fox, offshore activities coordinator for Shell Oil Co. in New Orleans.

Shell had announced plans last year to drill three to five wells in the mid-Atlantic area, but the company said yesterday that it has no plans to drill additional wells at this time.

One oil industry official said yesterday that the action casts doubt over future mid-Atlantic coast exploration. But a Shell spokesman said the company is not necessarily abandoning the Atlantic outer continental shelf.

"It's too early for us to write off the mid-Atlantic area as a failure," Fox added. "The oil industry will continue to look at this area in the future." For the time being, however, current oil industry economics, including declining prices, discourage high-risk, high-cost exploration, according to industry analysts.

Shell took the risk in its mid-Atlantic venture because, although there was a "very small likelihood of success, the potential payoff could have been huge," according to one oil industry analyst.

The drilling effort was "what you call a rank, new-field wildcat or, in the parlance of the track, a real long shot," said Sanford Margoshes, an oil analyst for Shearson/American Express Inc. "The odds of success were no more than 2 out of 100. But Shell was willing to drill with such poor odds because the size of the structures suggested that, if they struck oil, it would be an absolute bonanza and extremely profitable.

"Shell also had a commanding lease position," Margoshes added. "So if they were successful, a lot of other companies would have scurried to get positions, but Shell would have been holding all the cards."

The Discoverer Seven Seas, a 534-foot, state-of-the-art drill ship under lease to Shell, established a world record by drilling the group's third well in this area in 6,952 feet of water, a company spokesman said.

"There had never been anything approaching these depths before in the United States," a Shell spokesman said. "We developed new technology for the drilling because the water was so much deeper than what had ever been attempted before."

The Discoverer Seven Seas "encountered no commercial quantities of oil and gas," Fox said. But because such information is closely guarded in the industry, Fox declined to say whether the crews had struck a dry hole.

"Geological data obtained from the drilling program will be studied for planning of possible future drilling programs," a company press release said. "Important new drilling technology was developed and proved reliable at world-record water depths."

Leases for the first three wells were jointly purchased by Shell Offshore Inc., Amoco Production Co. and Sun Exploration and Production Co. The lease for the fourth well was purchased by Shell, Amoco and Murphy Oil Co.

Other energy companies also leasing offshore tracts from New York to North Carolina, including 21 off Virginia, have been "watching Shell to see if they had encouraging signs here," said J. B. Jackson Jr., the outer continental shelf activities coordinator for Virginia. Without such signs, drilling probably will be put on hold "until the right conditions come along," Jackson said.

"With the economic situation the way it is and the oil glut on, the oil companies will move to where there are proven resources," Jackson said. "I think the oil companies will come back to this area, but not in the near future."

"This was a frontier area with very deep water," a Shell spokesman explained. "If economic conditions change -- like the price of oil goes up -- we might come back."

Since 1976, more than 30 exploratory wells in the Baltimore Canyon, an underwater geologic formation running in a banana shape from Long Island, N.Y., to North Carolina's Outer Banks, have failed to reach a single oil and gas deposit worth exploiting.

"Shell and its partners didn't say they found no oil," Jackson, of Virginia's outer continental shelf office, said. "They just said they didn't find any deposits of commercially feasible quantities."

The eight-year-old, $60 million drilling ship, built in Japan and leased by Shell from Sonat Offshore Drilling Inc. of Houston, will sail from the mid-Atlantic to the Gulf of Mexico to drill exploratory wells in an initial water depth of 2,400 feet, a Shell spokesman said.