Touring the wine country of California has become increasingly popular, so a few guidelines are appropriate.

Go on weekdays, if possible, rather than on weekends. Weekends attract large crowds, making the tours less pleasant. On weekends also, many wineries limit wine-tasting while permitting unlimited tasting on weekdays.

Tours take from 20 minutes to an hour, depending on the winery, and usually are given at scheduled intervals between about 9:30 a.m. and 4 p.m.

Best time to visit is in the harvest season in the fall, when you can watch the grapes being brought in and processed.

Some wineries operate tasting rooms far from their wineries. At these, there are no tours. You simply taste, and if you want to buy a bottle or two, the management stands ready to accommodate you.

Don't expect to spend the day guzzling free wine in the tasting rooms. You are allowed a decent time, but tasting is intended to acquaint you with various wines, not get you drunk.

If you want to stay in the valley, make reservations well ahead of time. For information on tours and accommodations, consult a travel agent, a guidebook, or write to the appropriate chambers of commerce" St. Helena Chamber of Commerce, Box 124, St. Helena, Calif., 94574; Napa Chamber of Commerce, 1900 Jefferson St., P.O. Box 636, Napa, Calif. 94558

For a free booklet which lists all wineries in California that offer public tours, write for "California's Wine Wonderland" to The Wine Institute, 165 Post St., San Francisco, Calif. 94108. Enclose a business-size, self-addressed envelope.