Two decades and four Beatles ago ...

A modified form of Beatlemania is upon us again. The current wave of Beatles nostalgia - from Beatles anniversary segments on TV news shows to a radio station converting to Beatles-only programming - is based on the fact that this is the 20th anniversary of their first live appearance in America. Riding the crest of this wave is the theatrical release of ''The Compleat Beatles.'' Originally made for home video cassettes, this film is the first of its kind to get general movie-theater bookings.

In either form, ''The Compleat Beatles'' is an incisive portrait of a phenomenon of the 1960s. As narrator Malcolm McDowell points out, ''The 1970s and beyond were only to feel their influence.''

''The Compleat Beatles'' is not merely a fan-film. It is a serious study of the formation of a rock group, the influences of family and environment as well as their musical roots. Director Montgomery delves into the social differences between the middle-class skiffle-addicts of London and the lower-class fans of Liverpool who got their inspiration from rhythm-and-blues records brought back from American gulf ports by Liverpool merchant mariners.

The film takes the Beatles from their home base in Liverpool to Hamburg, where they honed their craft, and then back home to such clubs as the Cavern, where the filmmakers managed to dig up early footage of the group actually performing before they became famous. Family snapshots of all the Beatles, along with interviews with those who knew them ''when,'' give the otherwise slickly professional film a homey touch. One learns not only the origins of the individuals in the group, but one gets to know the origins of their music as well. While there is an obvious effort to minimize the scandals (the Beatles's involvement with police, drugs, and transcendental meditation; John's relationship with Yoko; Brian Epstein's role; the divorces; etc.), the film cannot totally ignore such events. But it keeps them in proper perspective.

Aside from the marvelous snippets of Beatles music (director Montgomery told me that he made stereo copies of the music from Captitol Records masters), there is superb footage from record promos which have not been seen since the 1960s. If there are errors - and there is a bit of manipulation of dates and events for dramatic purposes - they are excusable.

Perhaps the most informative and revealing segments of the film are the interviews with musical director/producer George Martin, the man responsible for much of what we know today as ''the Beatles sound.'' In the beginning, the musically-untrained Beatles had to hum their tunes to him for transcribing. With utter restraint and modesty, he nevertheless reveals much about his own influence on Beatle music.

George Martin is also an accurate interpreter of the impact which the Beatles have had on our society. ''The great thing about the Beatles,'' he says, ''is that they were of their time. Their timing was right. They didn't choose it; somebody chose it for them. But it was right and they left their mark in history because of it. I think they expressed the mood of the people of their own generation.''

According to director Montgomery, the Beatles ''have finally matured to the point where they can accept the fact that they will always be Beatles no matter what else they do.'' Next time he does a film about the Beatles, he expects to be able to get the surviving Beatles to appear in it. They refused this time around.

The $69.95 MGM/UA home video, released in October 1982, is still available in stereo cassette form; the film is currently in release through TeleCulture in 20 major cities across the country. Both are based, in part, on a two-volume book with the same title, produced by Delilah Communications. Delilah Films, with executive producers Jeannie Sakol and producer Stephanie Bennett, produced the film, which was directed by Patrick Montgomery.

I have both attended a theatrical performance of ''The Compleat Beatles'' and viewed the video cassette at home. The experiences are totally different.

Although the film itself is much sharper on the small-screen home TV than in its blown-up movie form, the sound in the theater was better because of the Dolby and stereo sound equipment (less than 5 percent of current VCRs in use offer stereo sound).

What was missing at home, too, was the group experience, the sense of community, the mass appreciation which was always so much a part of the Beatles experience.

Here I must explain that there is a rather special nostalgia attached to this film for me since, earlier in my career as the publisher and editor of entertainment magazines for young people, I published a ''one-shot'' magazine about them when they first arrived in the United States. I later traveled with the Beatles on their last two tours of the U.S. So I can vouch for the fact that the shrieks of ecstasy, the mass hysteria, the group madness which seemed to engulf a whole generation are not exaggerated one bit in the film. The segment where Ringo tries to leave his home, besieged by screaming fans, is typical of the kind of irrational adulation always accorded the group, referred to by their entourage as ''the boys.''

I was especially fascinated by the segment in the film on their last concert at San Francisco's Candlestick Park. As it flashed on the screen, I was reminded of a very personal experience there - the frightening moments at the end of the concert when the Beatles' security guards seated me and three other reporters in the Beatles limousine and sent it into the screaming crowd of girls outside the ballpark dressing rooms. It wasn't until the car was halted by the shrieking fans that I realized we were being used as decoys while the Beatles were smuggled out by another route.

We quickly locked all the doors and sped off for the airport, fortunate to escape the wrath of fans scorned.

''The Compleat Beatles,'' while not actually complete (there are holes in their story which only they can fill out), is the Beatles story as complete as anyone can make it at this stage in their careers. It tells the story in both audio and visual, something no single book or record can match.