When a 40-year-old Fairfax County scuba diver first saw the rusting hulk of a German submarine on the ocean floor off North Carolina more than a year ago, he knew he had a "helluva salvage project."

Dave Bluett, the diver and a computer specialist at Computer Sciences Corp. in Falls Church, didn't want just a small souvenir form the 220-foot U-boat to show he had been down there. He wanted one of the sub's 850-pound manganese-bronze propellers.

"It was a fabulous challenge to all of us to raise this thing so that other people might see it," said Fran Gibel, one of Bluett's colleagues in the venture. "Even more so because it took over a year to retrieve it. You could say the propeller was Dave's Moby dick."

Bluett, who has been diving for seven years and describes the sport as a "broad-based natural high," said he found his sunken treasure amazingly stubborn and fought it with 50-ton hydraulic jacks, liquid carhon dioxide and muriatic acid, all without seccess.

The submarine Rathre, according to a report filed in 1971 by marine scientists at Duke University, was a member of one of many German U-boat wolfpacks that sank at least 55 Allied merchant ships in the Graveyard of the Atlantic off the North Carolina outer Banks in the first six months of 1942.

"She [the Aathre] left a U-boat pen in Saint-Nazaire in April of '42." said 64-year old Howard Caulk of Silver Spring; who accompanied Bluett on many dives for the propeller. "She attacked the Coast Guard cutter Icarus, but her torpedoes wouldn't work, and the Icarus sunk her with depth charges."

Bluett, of 8137 Prescott Dr. in Vienna; Caulk, a solar astronomer from the Goddard Space Flight Center; and Gibel, a 30-year-old free lance public relations consultant, returned to the sub in September 1978 with blueprints supplied by U.S. Navy researchers.

But the five-foot propeller, its broad blades encrusted with barnacles, wasn't raised until two weeks ago.

Rough seas and unpredictable storms cancelled at least eight dives, Caulk said, and when the divers did get into the water, they encountered a host to other obstacles.

A 15-foot nurse shark, harmless but nonetheless disconcerting, prowled the clear, 80-degree waters near the wreck. The Rathre also carried a number of armed torpedoes, one of which was protruding from an aft firing tube 10 feet from the propeller.

"Sen. Lowell Weicker of Connecticut apparently made a dive near the wreck on Labor Day of 1978," Bluett said. "He didn't like the idea of us tampering with the vessel under those circumstances."

The Republican senator, an aide said yesterday, has told the Navy he is concerned that the torpedoes pose an "imminent danger" and has suggested that the sub be destroyed.

But Caulk dismissed the danger of an explosion.

They (torpedoes) "didn't work for the Germans in '42, so why should they work now?" he asked. "They've had 37 years to go off, so we just ignored them."

The Rathre was sunk in 105 feet of water 30 miles off Morehead City, N.C.

Bluett said his team didn't want to mark the wreck with buoys and expose it to other salvagers, so they used electronic navigation gear and depth finders to relocate the site each time they went out.

He said they spent $1,000 chartering boats and another $500 on tools.

The divers frequently suffered nitrogen narcosis, a "booze-drunk light-headedness" that made decision-making difficult, Bluett said.

"We could only stay down for 20 minutes at a time if we wanted to surface immediately," Bluett said.

Gibel and Caulk explained that if they stayed down for 40 minutes, they had to remain at 20 feet for two minutes and 10 feet for 21 minutes before surfacing in order to decompress and avoid the bends, a potentially fatal build-up of nitrogen bubbles in the bloodstream or body tissues.

In late 1978, with the divers frequently working until they were short on air, 30- and 50-ton hydraulic jacks loaned from the Maryland Ship and Drydock Co. failed to free the propeller from its shafts, Bluett said.

Last spring, they tried to push the propeller off with air-powered chisels, loosen it with muriatic acid and shrink the shaft with super-cold liquid carbon dioxide. All failed.

Early last month, Bluett said, he was ready to admit "this things got me beat."

But he went down once more on Sept. 29 with six spreaders he had made that, with three metal turnbuckles could apply 120 tons of pressure on the balky prop.

"The damn thing started moving," Bluett recalled. "I really couldn't believe it."

After freeing their corroded prize the trio hooded several air bags to the propeller to float it then hauled it aboard a trawler.

Millard Midget, a diver who claims salvagers such as Bluett are destroying sunken srtifacts for other divers, said: "They've really defaced that wreck." s

But Bluett defended his effort as a service to those who can't dive to see such treasures.

"Now instead of just a handful of divers almost anyone can see it," Bluett said. The team plans to exhibit the propeller at the Inward to the Sea Festival at George Washington University next Saturday.