Virtually everyone - still in 1984 - has something to say about the Beatles. * ''They changed the entire face of popular music,'' says a Scottish businessman in his 50s - launching into a long and favorable account of their beginnings in Liverpool, the moribund state of pop music in the early '60s, and their extraordinary conquest of Britain, Europe, America, Japan, Australia, and the world.
* A mechanical engineer in his early 30s, whose taste now leans more toward Grand Opera, confesses to a fondness for their music when at school - and also to a change of haircut.
* ''I was in my last year at high school,'' says an Austrian classical pianist and musicologist. ''Though I was not especially interested in them, you just could not avoid being conscious of them at that time.'' In retrospect, he says, theirs may be ''the representative music of our time.''
* A London art historian who actually came to know John Lennon and Paul McCartney a little finds that journalists still hang on his words as a result. ''I remember it as a period of great excitement. There is nothing like it today. The thing was, it was happening in Britain, not America. It wasn't even in London that it started.''
To some, of course, theirs was scarcely the music of the spheres. Even in their home city there remain dissenters. It took years of campaigning before Liverpool's governing council finally voted (in 1981, and by the narrowest majority) to name one new street after each of the ''Fab Four.'' At that time, an opposing councilor (unwittingly getting two for the price of one) could not resist commenting that ''the only member of the Beatles I would honor would be George McCartney.''
Yet now, a mere three years later, Liverpool has paid homage to Paul McCartney, George Harrison, John Lennon, and Ringo Starr with the opening of a permanent Beatles museum - complemented by a summer-long exhibition called ''The Art of the Beatles'' at the Walker Art Gallery here through Sept. 30.
The museum, ''Beatle City,'' is housed in a freshly refurbished building near the city center - and boasts, according to its advertising, ''over 1,000 absolutely original, authentic exhibits.'' Its facade is based on the famous ''Yellow Submarine.''
Presented as a simple fairy tale, the narrative inside chronicles the group's rise and fall, from press notices of their births to the shooting of Lennon in New York in 1980. Progressing from the damp obscurity of Liverpool clubland (the original ''Cavern'' is ingeniously suggested by a film clip and mock-up), it moves on to the creatively stretching demands of playing in disreputable parts of Hamburg, and finally to the hectic years of world renown and the endless rounds of increasingly scream-drowned performances.
There was a tendency, as their fame spread, to read them as more experienced or sophisticated than they actually were. One writer who went with them on their two last tours in the States commented that they were basically rather innocent and even naive at that time. They were also, in varying degrees, either earnest or curious, if somewhat untouched by education: That, self-imposed, was still to come.
But schoolboy-witty they were. The museum shows part of one of their laugh-a-minute press ''conferences'' on film. A reporter yells, ''When are you going to get a haircut?'' ''We had one yesterday,'' the replies bounce back. (And, with hindsight, one can see they spoke the truth: Those famous heads were immaculately groomed.)
On another occasion they were asked, ''When are you going to retire, fellas?'' Answer: ''In about 10 minutes.'' On another, ''What do you call your hairstyles?'' Answer: ''Arthur.''
But things became a bit more serious after Lennon had been requoted in the States, from an interview printed in Britain, comparing the popularity of Christianity unfavorably with that of the Beatles. In essence, he pointed out later, he meant that interest in religion was waning - a viewpoint some found objectively fair. Others, however, turned the comment into a major furor. At a Chicago press conference called to sort out the mess, the question came: ''To what do you ascribe your immense popularity?'' The reply was unflippant and - quite tellingly - baffled: ''If you want an honest answer - none of us know at all.''
The new Liverpool museum scarcely mentions this episode - at the time an excitable affair. It is more concerned, on the whole, with the sheer delight the Beatles gave countless people.
The aim of ''Beatle City'' is to be an effectively staged experience reflective of the Beatles' life and times. Yet when manager Roger White describes it as a ''vivid and significant slice of British social history,'' he cannot be taken too profoundly. Here, the innocent ''image'' of the four ''mop-tops'' with guitars and drums is the main theme - with little attention given to marriage breakups, flirtation with Indian mystics of dubious motivation , and the various developments of each of the four once the party was over.
In fact, the only slightly controversial moments in the tale are touched on lightly: The use of hallucinogenic drugs is merely mentioned. It can be argued, of course, that although their words and music were definitely affected by the drug culture of their times, the impact has often been exaggerated by too earnest interpreters. ''Lucy in the Sky With Diamonds,'' for instance, originated in a picture by Lennon's infant son of a school friend whom he identified by the since famous phrase. The initials ''LSD'' were pure coincidence, we are assured. Often indeed, the nonsense words of the songs were no more suggestive of the darker side of things than were Lewis Carroll's - a writer who was a favorite of Queen Victoria as well as of Lennon.
So far, the three surviving Beatles have had nothing to do with the museum, and have not visited it. ''We haven't asked them for anything,'' says the museum's ebullient and professional archivist, Helen Simpson, adding that ''we have offered them a private viewing.'' The family of their friend and manager Brian Epstein, however, approving the museum's amiable approach to Beatles ''history,'' presented a generous amount of memorabilia - and Mr. Epstein's mother, to the approval of all the sometimes contentious factions involved in Beatle history, officially opened ''Beatle City.''
In the main, the museum appears to have gotten the atmosphere about right. The Beatles were an energetic and funny breath of fresh air - and a great deal less weird or disruptive than many a group to come afterward.
By contrast, the summer ''Art of the Beatles'' exhibition, while it also dwells on the happy surface, delves a little deeper, through a continuously shown video called ''The Compleat Beatles.'' In some other features, too, this exhibition upstages the permanent ''Beatle City.'' The simulated '60s bedroom of a teen-age girl fan, for instance, is common to the exhibitions. It is particularly well done in this temporary show - complete with Beatles wallpaper, a miniskirt decorated with Beatles heads, a Beatles jigsaw puzzle, a Beatles bedspread, and a Beatles scrapbook.
Here, too, there is more music. While ''Beatle City'' is noticeably hampered by highly restrictive copyrights on use of both music and film, this exhibition seems freer. As the visitor progresses nostalgically or educatively (depending on age) around the display of portraits, record sleeves, drum logo designs, ads for Beatles boots, publicity photos, caricatures, and sculptures, the strains of ''Nothing's Goin' to Change My World'' lilts plaintively in the background - along with ''Lovely Rita,'' ''Michelle,'' ''Blackbird Singing in the Dead of Night,'' and other tunes.
As for the ''art'' connected with the Beatles, the show reveals quite a degree of serious attention given to them by painters as diverse as John Bratby, Richard Hamilton, and Peter Blake. Even Max Ernst made an insectival and surreal comment. John Lennon's art is even given some space - after all, as the catalog points out, he had been an art student once.
Taken in its entirety, this is an exhibition about imagemaking. The Beatles image has lasted no less than the music - although the exhibition makes clear that, while much of the music shows a striking resistance to becoming dated, the images are increasingly period things.
In the end, both exhibitions make clear the extent to which the group completely revolutioned the meaning of the word ''popularity'' - and by no means only in terms of unhinging the masses of adolescent females gathered into far-flung stadiums in the '60s. The real innovations came in greatly extending the range, inventiveness, and imagination of pop music; in bridging generation gaps with an irresistibly catchy code of melody; in demolishing class barriers of taste by an inconsequential mix of charm, wacky wordplay, and a fairly outrageous lack of pretension; in making music that (as one of today's teen-age Beatles admirers says) is ''good both to dance and listen to''; and (as music critic Richard Mabey wrote) in almost single-handedly ''breaking the intellectuals' boycott of popular music.''
Above all, they have lasted, as no other pop group has, with remarkable freshness in the popular imagination. Asked recently by their teacher to make a graph of favorite pop groups, a class of 11- and 12-year-olds in a deprived urban area of England put the Beatles on top.
Asked why, several of these children praised the Beatles for singing clearly understandable words. One commented that ''I like them because they were very versatile with their songs, their music was always brilliant, and it went with each song perfectly.'' Another remarked simply that ''they always seem to be happy,'' to which another added that ''they don't jump about mad; they just dance their own way.''