It's the fastest "can line" in the world.

When running at full capacity, a production line in the Anheuser-Busch Inc. brewery here fills 1,650 cans a minute with Budweiser. That's more than a case per second of the brew, which is shipped throughout Virginia, to the District, and to parts of Maryland and the Carolinas.

A short distance away by monorail from the most modern beer plant on the East Coast is Busch Gardens, a family entertainment park that opened in 1975 and which is expected to attract more than 2 million visitors during the 1977 season, starting today.

Adjacent to the beer factory is a 116-acre Busch corporate center, planned for offices and light industry. Among tenants will be James City County, which will move some of its offices to a new government center here.

And stretching across 2,900 acres between the brewery, office park Busch Gardens and the James River is a new residential and resort community called "Kingsmill," the beer manufacturer's initial residential business venture which may be home for 10,000 people a decade from now.

Taken together, these diverse operations add up to a 3,600-acre complex that represents the largest investment by Anheuser-Busch anywhere in the nation -- including St. Louis, where the world's largest brewer of beer was founded in 1852.

According to vice president Dennis P. Long, whose responsibilities include industrial products and the theme parks. Anheuser-Busch already has invested some $150 million in the Williamsburg area and "it will grow considerably higher than that."

Later this year, Busch officers will consider plans to double the capacity of the brewer here, which now can produce 2.7 million barrels a year. A decision to expand would make the Williamsburg factory the largest single brewery on the East Coast.

Beer has been the centerpiece of Anheuser-Busch enterprises since a small firm was started by Georg Schneider in St. Louis, a company that faced insolvency in five years and was rescued by a competitor with a loan from Eberhard Anheuser. A daughter of Anheuser married Adolphus Busch, an immigrant brewer's salesman, who really put the company on a sound basis and began broader beer marketing with the industry's first fleet of refrigerated freight cars; the beer company remains in the rail business today as owner of Manufacturers Railway Co., a local St. Louis railroad, and St. Louis Refrigerator Car Co., which repairs and operates freight cars.

Over the years, Anheuser-Busch has "backed into" a number of other businesses, as part of its drive to promote beer consumption or in reaction to prohibition. Amusement parks have been built near breweries; expansion into yeast manufacturing during prohibition developed an industrial products division; the St. Louis Cardinals baseball team was acquired in 1953 and is an integral part of marketing through sponsorship of broadcasts for the Cardinal' games.

In more recent years, Anheuser-Busch management has come to view its diversification in a different light -- as a method of continuing growth by the overall company when increases in bee output level off, ending the heavy performance of recent years.

One Busch officer said the need for diversification was seen in the late 1960s, when officers began to expect a plateau in the beer business would be reached by the late 1970s.

Anheuser-Busch actually suffered a significant interruption to steady growth in beer output last year -- but that was related mostly to a three-month strike. Beer sales volumes fell to 29.1 million barrels compared with the record 35.2 million barrels in 1975 and Busch's share of market fell to 19 per cent from 23 per cent.

This decline took place in a year during which Busch completed a new brewery at Fairfield, Calif., boosting output capacity to 42 million barrels -- about 15 million barrels higher than the capacity of the No. 2 beer maker, Jos, Schlitz Brewing Co.

Anheuser-Busch revenues last year fell to $1.8 billion compared with more than $2 billion in 1975 and profits sagged by 35 per cent to $55.4 million ($1.23 a share) from record 1971 earnings of $84.7 million (1.88). In the fourth-quarter, Busch wrote off $10 million for discontinuing its continuously unprofitable Busch Gardens in Los Angeles, which is being converted into a bird sanctuary and park.