AMERICA HAS gone "MASH" mad.

"MASH" reruns are defeating television king Walter Cronkite in the Arbitron ratings by about 2-to-1 in New York, Los Angeles, and other major cities. These reruns, released into non-network syndication for the first time this season, are now broadcast in more than 140 cities.

At the same time, CBS' current "MASH" episodes rank fourth in national popularity, according to Nielsen figures.

In Washington -- home of the military and political leaders so disliked by battle surgeon Hawkeye Pierce and his Army-baiting buddies -- Arbitron figures show the "MASH" and its reruns are seven of the top 16 shows in terms of total audience attracted. Only "60 Minutes" outdraws current "MASH" episodes, and the repeats beat the newest offerings of such prime-time stalwarts as "Archie Bunker's Place," "Charlie's Angels" and "Mork and Mindy."

A top national hit for eight straight years, "MASH" next season will trail only "The Waltons" as television's longest-running continuous prime-time series. "60 Minutes" has been on the air since 1968, but not continuously, and "All in the Family" premiered one year before "MASH" but last year essentially changed into a new show.

"MASH" has lasted three times longer than the Korean War it depicts and just earned the addtional distinction of helping America laugh about its Vietnam trauma. All three networks now plan Vietnam-based series built -- at least partly -- around the "MASH" experience.

NBC presented last week the pilot of "6 O'Clock Follies," which follows the adventures of armed forces television correspondents in Southeast Asia. Although network officials call it "MASH-like," co-producers Norman Steinberg and Marvin Kupfer say, "You can't be funny about Vietnam. This will have a harder edge to the humor. "If 'MASH' was progress beyond 'Hogan's Heroes,' then we hope to represent progress beyond 'MASH.'"

The CBS Vietnam offering, tentatively entitled "Bureau," is a saga of wire-service reporters. "We think this show will appeal to the same audience as 'MASH' does," CBS Vice President for Comedy Development Andy Siegel has told reporters. But Bob Daly, president of CBS Entertainment, says "Bureau" will be closer to another CBS hit, "Lou Grant." "We don't want to hurt 'MASH' in any way," he says. "That's one reason we changed "Bureau" from a half-hour pure comedy into an hour-long drama with comedy overtones."

An ABC spokeswoman says their "Bringing It Home," the story of two Vietnam war correspondents, "is in the very early stages of development." She adds that it is too early to know what the possible relationship to "MASH" might be.

"MASH" began as a failure.

Richard Hooker (the name is his description of his golf game; he wants to protect his privacy) is a Maine surgeon drafted during the Korean War. Nothing abnormal occurred during his duty overseas in a Mobil Army Surgical Hospital. He never considered writing about his experiences, and he took no notes. He returned safely to his hometown, which is, he says, "so small you have to pay taxes to spend money."

In the late 1950s, Hooker picked up pen and paper. He merely described people and circumstances he'd known. The hero, Hawkeye Pierce, was modeled after himself.

A friend showed Hooker magazine articles on how to get your book published, and in 1962 he got an agent. But the book received about 20 rejections over the next five years. Finally, in 1968 -- a decade after Hooker started writing -- William Morrow published "MASH." (Hollywood later added the asterisks between the letters.) Reviews in the trade press were good, and The New York Times called it "more than enough for a shooting script or a TV series."

The Times wasn't far off target. Although Hooker never considered a movie, Morrow had sent the manuscript to Academy Award winning screenwriter Ring Lardner Jr. Lardner, in turn, mailed it to agent-turned-movie-producer Ingo Preminger (brother of Otto), who took it to 20th-Century Fox. The studio reacted favorably, and hired Lardner to write the screenplay. As is standard in the film industry, the contract gave Fox ownership of any subsequent television program.

Fifteen directors turned down the Lardner screenplay because with American Vietnam battle deaths at several hundred a week, a comedy built around the seriously wounded didn't seem too promising. Finally, Fox hired Robert Altman, a middle-aged, ex-World War II bomber pilot with some television shows -- "Kraft Theater," "Bonanza," "Combat" -- and the feature film "The James Dean Story," to his credit. Halfway through making "MASH," stars Elliot Gould and Donald Sutherland reportedly tried to get Altman fired, but the movie was a surprise hit. "MASH" won the 1970 Grand Prize at Cannes, and received four Academy Award nominations, including best picture. The best picture award went to another Fox war movie, "Patton."

"MASH" earned approximately $40 million in 1970, making it one of the all-time move industry leaders.

The movie was fast-paced and loud, with no long sequences, no real plot and no overt political statement. In short, it had much in common with most television programs.

"We went to CBS because they were the best comedy network," says Bill Self, head of Fox television at the time ("All in the Family" and "The Mary Tyler Moore Show" were new CBS hits). "They had reservations about the language, the irreverence and the sex that had made the movie work. But they thought enough of it to give the go-ahead."

CBS saw the "MASH" pilot in late 1971. "After only one screening they decided to put it on the air," says Self. Television's only military program at the time was 'Hogan's Heroes," which depicted life in a Nazi prisoner-of-war camp as comfortable and fun.

Other new CBS shows were dying fast the fall of 1972 when the program premiered. "Anna and the King" and "The Sandy Duncan Show," scheduled right before and after "MASH," were off the air before the end of the year. To compound "MASH's" problems, its NBC and ABC opposition was "The Wonderful World of Disney" and "The FBI" both strong, popular programs.

"We were just about finished after only a few weeks," says a Fox official. "The cancellation order had already gone out from CBS. So we got our stars working the phones giving interviews to newspapers in key markets. It worked."

"One reason Fox stayed with it even though it wasn't getting terrific ratings was that it was appealing to young people with buying power, the group advertisers wanted," says Bert Metcalfe, "MASH's" original co-producer and now its executive producer.

"MASH" finished the 1972-1973 season 46th out of 75 prime-time network programs.

But at the same time, CBS officials saw something promising in "MASH."

"We had to be smart," says former CBS President Bob Wood. "We needed something for the 'in' group. This was the route we had to go."

For the 1973-1974 season, CBS decided to schedule "MASH" in television's then-most-desirable spot, Saturday evenings between superhits "All in the Family" and "The Mary Tyler Moore Show." "CBS decided to coddle us," says a "MASH" executive.

"MASH" finished the 1973-74 season as the nation's fourth-most-popular program and has been a ratings hit ever since.

In the meantime, author Hooker -- who started it all -- has played no role.

Soon after the television show started, he mailed Hollywood an unpublished chapter of his novel, but they never used it. "I think he's dead now," says a "MASH" official.

Still very much alive, Hooker says he "never became a millionaire from "MASH" and still has to work for a living." He watches the television show only infrequently, and doesn't think much of it. Others who served with Hooker's real-life "MASH" unit mirror his indifference. The surgeon after whom he modeled Trapper John McIntyre says he has "nothing special to say about 'MASH.'" And he's never seen "Trapper John, M.D.," last year's spinof from "MASH."

"MASH" transcends in popularity every other American statement about war. Books like Norman Mailer's "The Naked and the Dead" and Joseph Heller's "Catch-22," and innumerable war movies have won critical acclaim and a durable following, yet all failed to acquire the continual mass appeal that only television can provide. But even in the face of such success, broadcast officials are curiously unable to pinpoint what lies behind the "MASH phenomenon.

"If I knew what we were doing right, I'd quit and start doing it on a lot of other shows," say John Rappaport, current co-producer of "MASH."

Still, four explanations for "MASH's" popularity can be identified. First, the "relevancy" programs of the early 1970s all remained extraordinaryly strong. Television ratings leaders in the late 1960s -- such as "Gomer Pyle," "Dean Martin," "Bonanza" -- were rural, western and completely nonserious. All were taken off the air and replaced by "All in the Family," "Sanford and Son," "Mash" and other socially relevant shows, which went on to dominate the decade. Of the 1973-74 Nielsen top 10, all but "Cannon" and "Kojak" still flourish, either in their originial form, in a modification, or in a spinoff.

"MASH" also tapped in 1970s' turn to nostalgia. "It offered escapism to the '50s, to the time when wars were still neat and won by Americans," says media scholar Arthur Asa Berger. "Of course, that really wasn't true, but that's how people like to believe it was."

Second, the departure of stars has made "Mash" stronger. Only the actors playing Hawkeye Pierce and Hot Lips Houlihan have served "MASH" for the duration. Jamie Farr appeared as Klinger in a guest slot during the first year, and did so well he became a regular. But actors playing Lt. Col. Henry Blake, Maj. Frank Burns, Cpl. Radar O'Reilly, and Capt. Trapper John McIntyre left to pursue careers elsewhere. Such attrition normally kills a television show, no matter how popular. "But because of the combat setting, replacements were easy and made sense," says Rappaport. "In a war, soliders always come and go."

"MASH" replacements have always been entirely new characters -- not simply new faces put in the same role, the way most television programs handle star defections. "We learned from the movies' experience with James Bond and Inspector Clouseau," Rappaport explains. "You can't go against what the audience expects."

Only the departure of Wayne Rogers, who played Trapper John, blemished "MASH's" behind-the-scenes happy-family image. Elliott Gould, playing Trapper, dominated the movie, and Metcalfe says that "the roles of Hawkeye and Trapper were totally interchangeable when we started. It was a tossup. But Alan Alda, who plays Hawkeye, developed a strong relationship with the writers, and the show went that way." According to press accounts, Rogers simply walked off the set after three seasons.

This past season saw the departure of Radar O'Reilly -- played by Gary Burghoff, the only actor to appear in both the movie and the television versions. Instead of bringing in a new company clerk, Metcalfe simply changed Klinger, the GI who hoped feminine apparel would win him a psychological discharge from the Army. Now Klinger wears his uniform and has accepted Radar's old assignment. "We had played out the whole women's clothing craziness," says Metcalfe.

Of course, future visits by past stars remain a possibility. Colonel Blake's body was never discovered; his helicopter merely "went down." And Trapper John, Frank Burns and Radar never fully escaped the long reach of Uncle Sam.

Third, contrary to its antiwar reputation, "MASH" has never been controversial. "We've never gone against the accepted wisdom, we've always ridden it," Metcalfe acknowledges. "We're controversial in the sense that we go against accepted television form and take positions contrary to the leadership establishment."

Even the "MASH" movie wasn't really antiwar. "In fact, it is in a sense pro-war, in that the authority defied or sabotaged is through its stupidity hindering the successful waging of the war by undermining the efficiency of an organization (the hospital unit) whose insanely dual purpose is to save life and to patch lives up to be sent back for renewed destruction," writes Ivan Butler in "The War Film."

When the television "MASH" premiered, Variety sarcastically "commended" CBS "for its courage in bringing viewers the lighter side of the long-running Southeast Asian conflict."

The best measure of MASH's continual freedom from controversy is that the Veterans of Foreign Wars has never complained. Always quick to protect the military's image, the VFW claims to have recently prompted the Ford Motor Co. to yank a television commercial depicting Gen. George Patton. "I've never even heard criticism of "MASH" at any of our meetings or conventions," says a VFM spokesman.

"MASH" is in reality a comedy," says Reynolds. "To use a Radar expression, it's been anesthetized. But it's strong in comparison to what has gone on television. We don't show people dying in an easy way. It shows that war in general is the result of human folly and that there are no winners."

"Sure, it's realistic as far as it goes," says a GI whose life was saved by a MASH unit in Vietnam. "Even the joking really happened, but they could never show how grim it really was. The groans, screams and whimpering alone are enough to get you. If television showed that just once a year instead of 'The Wizard of Oz,' there'd never be another war."

Fourth, the quality of writing, production and acting has remained high. "I can't think of any show that has consistently turned out a better product than "MASH," says one advertising executive.

The first four years of "MASH" were written by Larry Gelbart, considered by most in the industry to be television's best writer (he left "MASH" in 1976 and returned to television last month with his new "United States" series on NBC). "On 'MASH' people show joy and wit," says Gelbart. "They don't suffer in a conventional television way. They show how to handle stress and strain. They're real." Subsequent writers have maintained the Gelbart tradition. Backing them is extensive research not often found in Hollywood. "We interviewed just about every MASH doctor and nurse we could find," says former executive producer Reynolds. "MASH" producers visited MASH units in Korea and crisscrossed the country in search of combat stories. "We are always asking doctors with MASH experience in Korea or Vietnam what they think of the show," says Metcalfe. "They tell us we have no idea how bizarre and crazy their nightmare really was." Metcalfe still gathers original material, and will be at a MASH unit's reunion in Chicago this May. "Sometimes we'd sit there and get excited about a story a doctor's telling us," says a former "MASH" producer. "We'd say, 'No, you should have acted like this and this,' and then we'd remember we were listening to the real thing."

Production costs for "MASH" are about $250,000 an episode, which is high, but not unusual. "We do everything on film, no tape, to maintain the flavor of the movie," says co-producer John Rappaport. "This makes it more difficult to edit, but it's worth it. We also use the one camera technique. We have to shoot some scenes several times to get all the angles we want. This costs more, but it gives us more freedom to show the scenes the way we want without other cameras getting in the way."

Critics hail the acting on "MASH" as among the best on television. "It was a combination of skill and a great deal of pure luck," says Metcalfe, who worked on the originial casting. "We were especially lucky that the chemistry worked so well."

"MASH," in turn, seems to bring out the best in actors. "We did a show where the Colonel and Charles were trapped in a tent together, both with mumps," says Rappaport, "The Colonel was angry and started towards Charles. 'What are you going to do?' Charles asked. 'I'll think about it when I get there,' the Colonel replied. Then Henry Morgan (who plays Colonel Potter) began an hysterically funny and strange walk that wasn't in the script. I asked him afterwards how he did it, and he explained that he'd taken one slipper off and walked trying to keep the other on. It made the scene. That sort of thing happens all the time."

"Unfortunately, most of my conclusions about "MASH" are fairly cynical," says Executive Producer Metcalfe. "The biggest tragedy is that the networks haven't learned from it. If it were starting out now, 'MASH' wouldn't survive. The networks wouldn't stay with it long enough for it to get its foot in. When you're dealing with a commerical broadcast system, you're dealing with greed."

Metcalfe warns that the new Vietnam successors to "MASH" will have constant interference from the network, sponsors and affiliates saying, "Make it funny, make it funny, don't make it too serious."

"In spite of what they've seen from us," he says, "they're still afraid."