Workmanship on nuclear submarines by the Electric Boat company was termed "shocking, incredible" and "negligent" yesterday at a House hearing where the Navy detailed flaws ranging from weak welds to plugs that rusted out, in one instance allowing sea water to rush into the engine room.

"The most distressing hearing in my 30 years in Congress," lamented Rep. Charles E. Bennett (D-Fla.), chairman of the seapower subcommittee, after hearing Vice Adm. Earl B. Fowler deliver a 25-page paper on problems at the Electric Boat yard at Groton, Conn.

Even though Fowler, commander of the Naval Sea Systems Command, claimed that the Navy was "on the downside of the problem," reactions of several subcommittee members raised the question of whether the Navy would be able to spend wisely the extra billions President Reagan has earmarked for building submarines and warships faster.

Fowler told the subcommittee that he will recommend to his superiors soon that the Mare Island shipyard in California be equipped to build nuclear attack subs, though not Trident missile submarines. He said the Navy would have to spend about $300 million for this shipyard expansion and add 7,500 civilians to its payroll.

Only the Electric Boat Division of General Dynamics and Newport News (Va.) Shipbuilding can produce nuclear attack subs, and only Electric Boat is capable of producing the giant Trident missile submarine, a setup that was criticized by Rep. Floyd Spence (R-S.C.), who complained that the government is being "helf captive."

Fowler admitted that the Navy as well as Electric Boat was to blame for foulups that have delayed delivery of the Los Angeles-class attack submarines and Trident missile subs.

"A sad commentary on our country," said Rep. Thomas F. Hartnett (R-S.C.) after hearing Fowler estimate that the first Trident sub will not be delivered until this December, two years late. "It shows an incapability to produce such a weapon."

The House seapower subcommittee has been the biggest booster in Congress of an expanded Navy shipbuilding program, and Bennett said that it is "a blot on my life" that he did not know, as chairman, how bad things were at Electric Boat.

Fowler, in testimony that Electric Boat has been invited to rebut next week, listed these problems in the nuclear submarine construction program:

Electric Boat mixed acceptable and unacceptable steel in its warehouse and then made welds with some of the unsatisfactory material.

After the steel mixup was discovered, Electric Boat could not find inspection records on many of the welds. The company then resorted to inspecting those welds it could reach.

Of 6,893 welds inspected on one submarine, 2,802 needed repair. Of 8,476 welds inspected on the first Trident, 2,772 needed to be strengthened.

Electric Boat used the wrong kind of metal for plugs on some attack submarines. In 1976, the base of one of these plugs rusted, allowing 400 gallons of sea water to rush into the engine room of a Los Angeles-class boat, which was docked at the time.

Electric Boat used the wrong kind of paint, and the Navy insisted that it be scraped off and replaced.

Fowler said that Electric Boat is trying to get the Navy to pay for the cost of such repairs, contending the money should come out of the building insurance fund issued by the Navy. The Navy is contesting the company's claim, Fowler said.

Fowler said that part of the problem was that the Navy "had a fragmented, piecemeal approach" to problems at Electric Boat. He stressed that the defects uncovered do not endanger the lives of submarine crews, primarily because the flaws discovered to date have been in the outer hulls of submarines, not the inside pressure hulls, which crews are housed.

However, Fowler said five nuclear attack submarines already at sea when the defects were discovered were ordered to reduce their diving depths. He said Electric Boat has not yet come up with a plan to identify and correct the possible flaws on those five submarines.

The subcommittee also was told that, although Electric Boat was not to blame, the turbines General Electric supplies for submarines developed cracks and the ones produced by Westinghouse proved to be out of balance.