What with 68,000 pubs in Britain, they are impossible to overlook and improbable to avoid, but for the unenlightened they can be unfathomable. In existence before both the Church and the Bank of England, they are a mine of form and ritual.

Perplexed me, for a long time. Hanging out in London and environs on and off for 20 years, and in public houses (as pubs are formally known) because that's where so many British do their hanging out, I was never quite sure what besides drinking is supposed to go on. What are the ancillary activities, possibilities and gaucheries? Or how do you even begin to choose between the public bar and the saloon bar?

Spending last summer in England with a 5-year-old daughter who appropriated my days, I spent the evenings finally, even necessarily, checking out pubs thoroughly.

First off, you decide between the public and the saloon bars. These co-exist as separate parts of more pubs than not, and your choice depends on your accent, clothes, sex, income, means of livelihood, taste in surroundings and, above all, social class. Coachmen and footmen to the public, m'lord to the saloon.

These days the saloon -- sometimes known as the lounge -- is patronized by those known in the public bar as toffs, defined by a friend -- who is a pub-going playwright -- as "smartly dressed people with high-toned accents."

Toffs pay a few pence more for their drinks and are provided improved social conditions: thick carpets, mahogany tables, chintz-covered chairs, perhaps a Constable reproduction and a horse brass or two, and almost invariably a collection box for charity.

In many public bars, you might think you were in a dingy country kitchen: wooden chairs, linoleum floors, formica tables, bleak lighting, beery colors and, on the walls, a dartboard, a pin-up calendar and an age-speckled picture of the Queen on a Horse.

Although some saloon customers -- old actors, failed real estate brokers -- wouldn't be caught dead in the public, there are gents in pin stripes who like to visit because it makes them feel like "one of the lads." But those who commonly patronize the public -- construction workers, drivers of large vehicles and gamekeepers -- wouldn't dream of going to the other, nor do they welcome toffs, tourists or women.

As pubs are the traditional domain of the middle and working classes -- the upper middle classes and beyond have people in for drinks -- so are they, at least primarily, of men. Recent studies have shown that the current pub clientele is about 85 percent male.

"Men are far too interested in talking about horse racing and football and the like to bother much about women," says Brewers' Society spokesman Kenneth Dunjohn, who also says women for their part are wont to find pubs "smelly."

Furthermore, says Dunjohn, "a large number of pubs have something of the air of gentlemen's clubs and the presence of too many women might spoil that."

But with more British women now working outside the home than in any Western European country except Denmark, there has been a recent development of cocktail bars, disco pubs, saloon-bar-only singles pubs, the wine bar and "theme" pubs to attract their trade.

None of these digressions, however, is likely to be graced by the barmaid of an Englishman's dreams, a buxom blonde tease who is always good-natured and sympathetic (unlike she who is at home) and inspiration for the pub-going euphemism, "I'm just going out to walk the dog."

At the same time, the barmaid is untouchable, and as you must be respectful to her always, so must you be to the man who runs the show, variously known as the publican, landlord or, most preferred, the guv'nor. Nobody's waiter, he wields authority and sets tone.

Explains Richard Boston, one-time beer correspondent for the Guardian: "Like the schoolmaster in the classroom he is both referee and focal point of attention . . . Everyone is affected by the atmosphere he and his wife not the barmaid generate through their conversation and the kind of custom they encourage or discourage."

The guv'nor filters local gossip, knows who provides what service (above and below board), cashes checks, makes loans and sees that friends get you home if necessary. He often lives on the premises, and you should remember you're his guest.

Also to be shown deference before you can start sipping your beer are the regulars, whose orders will always be taken before yours, no slights intended.

The regular is the bedrock of the pub business and will likely have his regular drink presented in his regular glass without so much as an irregular verb being exchanged, and should you be occupying his regular place you will soon find yourself displaced, nuanced though the nudges will be. There are, says a London sociologist studying pub interactions, "very clear spatial delineations in pubs."

If this seems like a lot to wade through just to get a beer, don't think the beer is a simple matter either.

There are, first of all, some 1,200 brews to choose from nationwide, and then you have to decide whether you want it in a pint or half-pint glass.

In the saloon bar they usually opt for half-pints because -- says a house-painting rock 'n' roll drummer by name of Kevin who also served as guide -- "that's so much more tasteful than those pople next door who slurp down pints." Also acceptable in the saloon are gin and tonic, scotch, sherry and wine.

In the public bar, says Kevin, "it's mostly straight beer drinking, and bitter is the main one."

Bitter is, as the name suggests, the taste from a liberal dose of hops, and there is also mild -- more sugary and syrupy, brewed with darker malts and fewer hops and increasingly less favored.

Confounding the issue -- beyond black, creamy Guinness, which is a stout -- has been the introduction of lager on a mass scale in the last 20 years and, in response to that and other chemical wonders, the reactionary Campaign for Real Ale. (See related story, Page E3.)

Ale is, in fact, simply a malt brewed without hops, but the name sounds so much more authentic, and 25 percent of all beer now drunk in Britain (almost 11 billion pints a year) is the real stuff -- the yeast top fermented, the sediments retained and the flavors left untampered, delivered by pump systems rather than carbon dioxide pressure. It should be served at British room temperature of 55 to 60 degrees fahrenheit. But just ask for "a pint of ordinary," and you'll get the idea.

Drink in hand, you can join the activities. Foremost among them is chat. And there are curves there, too.

The purpose of pub conversation, says Richard Boston, "is to find areas of agreement and common ground. Confrontation and controversy are usually avoided."

Says the playwright: "It's very important to remember that no talk of any consequence ever takes place in an English pub; it's all endless trivia."

My own discovery has been that to be pleasant is the highest social ideal in Britain.

You'll always be safe discussing the weather, asking advice or offering a drink.

You can also play games -- the classics are darts, dominoes and shove ha'penny, the last of which dates from Tudor times and involves sliding coins across a highly polished surfaced. If you want to join in, you present yourself in a submissive sort of way -- you watch, you get a little show, you're asked if you'd like to "have a go."

Or you can eat.

Best choices and value are at lunch, and besides omnipresent potato chips (called crisps) and cardboard sandwiches, you can usually get sausages by themselves, with mashed potatoes, baked in rolls or encasing a hard-boiled egg (a Scotch egg).

Frequently available are shepherd's pie (minced meat in gravy under a mashed potato crust), steak and kidney pie and the all-purpose ploughman's lunch, which consists of a lump of bread, a dab of butter, a lump of cheese and a sprinkle of onions. Recent innovations include salads and what the English refer to as "continental dishes," such as moussaka, lasagna and quiche.

Or you can, as many do, sit and stare into space.

If you do socialize, you must buy a round -- not even a bounder wouldn't, although he might drink fast and expensive.

Other refinements of pub etiquette include:

* Always go to the bar when you want a drink.

* Pay cash.

* Don't tip, but you may show your appreciation by asking, "Will you have one yourself?" If he says he'll have a small sherry later, it basically means, "I'll keep the money, thanks a lot." Keep track of the "permitted hours of sale," which are stricter than anywhere outside the Moslem world and baffling to foreigners.

In London, most pubs are open from 11 a.m. to 3 p.m. and then from 5:30 to 11. In the country, it depends on local magistrates, and in some counties pubs open later and/or shut earlier. On Sundays, everywhere, the hours are noon to 2 and 7 to 10:30.

The "permitted hours" were introduced under the Defense of the Realm Act of 1915 as a temporary measure designed to keep munitions workers sober and at work. No British government since, according to the Economist, "has trusted its people to go back to work in the afternoon or to bed at night without stringent control of pub hours."

The result can be seen in the rituals: customers rushing to the bar during the last half-hour for three or four drinks; the ringing of bells to announce minutes to go before all that bonhomie will be turned off like a tap; the announcement of "Time gentlemen, please."

People do complain.

They also grouse that pubs are old-fashioned, dull, stilted, class-ridden and male-chauvinistic, and attendance declines annually. Beer sales have dropped 12 percent in the last five years. The National Union of Licensed Victualers warns that 10,000 pubs will have to close by 1992 if the remainder are to survive. The brewery industry predicts that a thousand pubs may close this year.

"The pub is under great threat," says the playwright. "The English are moving away from the tradition of using pubs as they used to. They're becoming more places of entertainment."

The threat is being met with departures on the order of Total Environment Control systems that employ tape machines to provide varying light and music intensities for different times of the day, and the theme pubs that are said to be an "American influence." The Dome (formerly the Bird in Hand) in Hampstead has been "themed" into a brasserie serving French food and cocktails, with a room for backgammon and chess, and the Ole Rangoon recreates a colonial plantation house, with lots of Taiwan wicker.

But whatever the mutations, the pub will never be extinct, not in a country where going out for a drink is a national pastime.

And, too, the pub operates in a dimension beyond the mere serving of drink. It's the meeting place of a community -- "the local" -- where cricket matches are organized, charity raffles held, repair jobs contracted, and where, within walking distance, loneliness, boredom and television can be escaped.

They are also guaranteed, in a cold climate, to be warm.