In America wine is cheap - and wine is forbidding. We all have a friend who can and will (and often must) tell us just how far west of the Mississippi you have to go for Coors to taste good, who knows exactly why Jack Daniels is not a bourbon, who can tell to the eyedropperful how much vermouth you put in a martini. And who says, when you mention wine, "I don't known anything about it. I've always wanted to learn."

There are lots of ways to learn - from college wine classes to winetasting societies, to getting together with a dozen friends and buying a bottle each from all the chateaux in Bordeaux.

But the way to have fun and learn about wine is by visiting a winery. You get a nice drive in the country; you get a tour that shows you how wine is made and bottled, you get to talk as much or as little as you want to people who know wine like your friend the Coors expert knows beer.

And you get to drink a lot of wine.

Expecially if you start with the Provenza winery, the largest and closest to D.C., and possibly the most convivial anywhere. Call ahead for reservations - Dr. and Mrs. Provenza, who conduct the tours like to have groups of 30 or so, and it may be a week before they can fit you in. A tour of Provenza, though, is worth the wait.

Tours start around 1 p.m., and you should allow a whole Friday or Saturday afternoon. Drive out New Hampshire Avenue, past the all-night drug stores and endless suburban ranchers and handprinted signs advertising yard sales, until you cross the Beltway and suddenly the road shrinks from four lines to two, the yard sales turn into farm stands selling homemade cider and apples so ripe and warm they smell like cooking applesauce. Then the houses turn to clapboard, then to bigger ranchers, then to mansion-ranchers, then to places so lost in the trees you wouldn't even know they were there except for the signs that say KENNELS or STABLES. Now the road shrinks again, to a single lane, slowly getting swallowed in falling leaves. When you reach Brighton Dam Road at the bottom up of Triadelphia Revervoir, slow down. Half a mile ahead is Green Bridge Road. Take a sharp right, then a left on the stony driveway, marked only by a mailbox that says PAUL. Keep riding on the stones until you see a building that looks like a big rent barn. That is the Provenza winery, producing 1000 gallons of wine a year.

Our group was met by Dr. Provenza, a slightly chunky, grayhaired man with a pleasant deadpan kind of humor - and a glass of wine.

"You go to one of those big California wineries," said Dr. Provenza, "and first of all the place looks like an oil refinery - this is our red, we make three wines red, white and rose - it looks like an oil refinery, all 20-inch pipes and thousand-gallon stainless-steel tanks. You get to seen some worker turn a valve here, some stuff goes there. They take you in and say, 'This is a crusher-stemmer, here's a press, here's a glass of wine, and there's the salesroom.'

"We're not permitted by law to sell wine in Maryland. So this is just good will; all we ask is that people make an appointment and not just drop in - that's why we don't have a sign or anything out front, drop-ins drive us crazy. Here, let me give you a little more of the red . . ."

A little more red, a couple glasses of a dry cold rose, a couple more of white . . . this is the world's most painless basic course in wine and winemaking.

Provenza wines are made from French hybrid grapes - French vines grafted onto American roots to assure a hardier stock. Many people prefer the traditional vinifera grapes. Dr. Provenza thinks the new hybrids make a good serviceable table wine.

"Take a bottle that's labeled by variety. Take a California Pinot Chardonnay. First of all, to label it, all they have to use is 51 per cent of the varietal grapes. The rest can be . . . other stuff. A lot of it comes in jugs, with a metal cap. Now you can't make wine with a metal cap. God won't let you. Unless you pasteurize it and ionize to preserve it. And a lot of the stuff in corked bottles is just jug wine in corked bottles, you can open it and leave it anywhere, it'll be just as good in a week or a month. You pop the cork on our wine, you'd better drink it, or put it in the refrigerator and drink it the next day. This is living wine . . .

"Of course, if you are willing to pay the price, you can get a bottle of 100 per cent Pinot Chardonnay from California - at $10, $12 a bottle. Our wine, depending on the store you buy it in, costs around $3 a bottle. With a good cork, with a lead capsule on the top imported from France, not a plastic one. You put your name on something, you want to do it right. The trouble is, the bottling is starting to cost more than the wine. But it has to be right. We get calls for jug wine - restaurants that will sell you a glass or carafe of wine want a jug of it to stick under the bar . . . They have to get it somewhere else."

More wine, and we join a tour that includes a Spaniard who looks like Herbert Marshall did 40 years ago, who owns a vineyard in France, and who knows everything there is to know: "We did our first planting in 1974, for our children, and this year we have our first appellation controllee . But the year is so bad we don't want to bottle. Buy no '77 Bordeaux, my friend. We are selling in bulk to the English; everything moves. They will be very happy English with all that Bordeaux this year."

By this time Mrs. Provenza has brought out trays of eggplant parmesan and something called Georgian cheesebread - homemade bread with muenster and bleu cheese melted inside. There's lots of food, which more or less sobers us up, and lots more wine, which does not.

"We always have some kind of food with wine. Beer you sit around and drink. Wine you drink with food," says Mrs. Provenza. "Right now, I'm making a lot of eggplant because we have so much coming out of the garden. I almost always make the cheese bread - it's so popular that I finally had to mimeograph the recipe so I could give it to people who asked for it. Sometimes, if I've been really busy that week you'll only get cheese - but it will be good cheese, and there will be enough of it."

Dr. Provenza is explaining the difficulty he has had with the neck label on his wine:

"A year or so ago the government announced a new regulation that you had to put the ingredients on the bottle. I didn't care - I'm proud of what goes into my wine. I put the ingredients on the neck label: 'grapes; sugar and yeast to ferment; potassium metabisulphite added as preservative.' Now all the wine in the world is made with potassium metabisulphite, but most people don't know that, they never saw the word, they can't pronounce it, and they kept asking the waiters in the restaurant what the hell it meant. And the government didn't decide to enforce the regulation. I thought I would take it off, if it bothers people. But then a couple of the restaurants that serve our wine are health food restaurants, and they liked the label, they liked to show the customers that there were no other chemicals in the wine. Or water - I could double my output if I watered my wine. If I didn't want to do it right . . .

"So, finally, I'm putting the ingredidents on a third label, on the back of the bottle; if you don't like it you can take if off."

One of us admires the color of the rose, and that delights Dr. Provenza.

"A winemaker works on the color - almost more than anything else. We like to get color and brilliancy in our wines. Come outside and look - I hate to look at wine under flourescent light. Outside is where we check color - it's better than the traditional method of using a candle, because . . .

"Look," he holds up the glass for us, wiping the frost that forms on it from the icy wine, "we do this at natural temperature, but if you wipe the haze off the glass . . . Look! You see, we like to turn the glass this way and that in the light, till you get the reflection of the leaves."

Stuffed with homemade bread, cheese and garden eggplant, and smiling from wine, everybody stands, glasses raised at the hills that are still full of grapes, looking at the nearby trees, tilting the glass till we get the reflection of the leaves to bounce around in the glass like points of light - that's the pleasure I remember most clearly from that pleasurably hazy afternoon.

Just remember two things call for an appointment, and never try to visit more than one winery in a single day. Unless you have a nondrinker along to drive home.