The nation's weapon-makers have concluded that the "never again" hang-over from Vietnam has faded to the point where they can profitably advertise how they could help the American military fight in distant lands.

Marching through armed services magazines, the aerospace trade press and general audience publications are ads that defense contractors themselves concede would have disturbed the public during and immediately after the war in Vietnam.

"We would have considered that ad insenitive two or three years ago," conceded William D. Perreault, Lockheed's vice president for corporate communications, referring to a two-page ad that runs a headline: "Helping to keep the eyes sharp and the talons strong. Lockheed believes the ad that might have been found offensive during Vietnam is now "comforting."

"It is comforting to the citizens to realize there are people doing this work and making substantial advances," he said.

In addition to advertising the breadth of its weaponry, Lockheed is among those defense contractors who are zeroing in on the Persian Gulf. "Introducing the Diego Garcia-Indian Ocean air shuttle," proclaims a recent ad ballyhooing how useful Lockheed's S3A Viking plane would be for delivering spare parts and other items from the American storehouse on Diego Garcia to aircraft carriers guarding Persian Gulf oil routes. The Viking can land on a carrier deck.

"Tomorrow's assault force is just over the horizon," states Rohr Marine Inc. in advertising a high-speed ship that could "open to assault four to five times the coastal sites that could be used by our Marine Corps today." Such a message would have been a lightning rod for trouble during Vietnam. #t"We do see a greater willingness to face the realities in protecting our interests overseas," said Larry Peeples, Rohr's public relations director, acknowledging that his company is responding to this changed mood. The way Rohr sees this new mood, Peeples said, is epitomized by the realization that "we can't back away like we did in the years of the Vietnam syndrome."

Teledyne Ryan Electronics, in an effort to get a piece of the new action as the Pentagon spends billions on Persian Gulf forces, is advertising how its equipment could help the Marines in "hitting the beach right on the button."

And Todd Shipyards Corp. is warning in its ads these days that the United States is so dependent on foreign oil and other minerals that it had better get busy building up its merchant fleet and Navy.

"How will we keep this island functioning without ships?" asks Todd in one full-page ad.

"That's an advocacy ad," said Robert J. Daniels, Todd's public relations director. "We're trying to influence the administration and the Congress to beef up the merchant marine and the Navy warships.

Another defense company executive, who did not wish to be quoted by name, said contractors, as well as trying to cash in on higher defense budgets and the Pentagon's newly aroused appetite for weaponry for intervening in distant trouble spots, also are under pressure by the armed services to advertise more.

"The customer," he said in referring to the Army, Navy, Air Force or Marine Corps, "often asks us to help sell the project to the administration and Congress through advertising."

The services are supposed to keep arm's length from the contractors on such matters, but in real life they often are allied in trying to influence a government decision.

Lockheed's ad about helping to keep the American Eagle's eyes sharp and talons strong appeared in general circulation magazines, including Time, and business magazines, including Business Week and Fortune. The company's narrower focused "product" ad on its Viking aircraft ran in the specialty press, including Proceedings, the Naval Institute magazine read widely by Navy officers.

Rohr's ad on amphibious assault appeared without charge in the magazine Sea Power as part of the package for joining the Navy League. Peeples said. The league champions Navy causes.

Pentagon executives acknowledge that their new emphasis on gearing up for Persian Gulf operations is a honeypot for defense contractors: an extra $30 billion over the next five years, on top of already high military budgets. This probably will impel weapons makers to continue advertising what they have to offer in this new arena.

One side effect of all the advertising could be to condition the public and federal decision-makers to the idea that intervening militarily in such distant areas would be an acceptable use of American power, despite the U.S. experience in Vietnam.