Because of a typographical error, the Hershey Foods Corp. share of U.S. candy sales was incorrect in a story on Mars Inc. in yesterday's editions. The correct figure for Hershey is about 23 percent.

The company is one of the largest advertisers in the world. It employs some 12,000 persons, who manufacture and sell close to one-third of all candy consumed in the United States each year, making it bigger in that business than Hershey Foods Corp.

Of particular interest to Washingtonians, the company - Mars Inc. - has its corporate headquarters in Northern Virginia. But few area business leaders or residents are aware of the Mars operation, despite its giant size.

By following a deliberate policy of staying out of the news, Mars has maintained an unusually low profile. Given its base in leak-prone metropolitan Washington, one could say its achievements in secrecy are particularly noteworthy.

But Business Week magazine, in an edition that will be published today, lifts some of the Mars corporate veil.

Mars, founded in Minnesota with a $400 investment in 1920, was started by candymaker Frank C. Mars. From a one-room factory in which he and his family lived in 1923, Mars struck on a recipe for a candy bar he called Milky Way. In one year, sales jumped from $72,800 to $792,000. By 1930, the company had become established in the candy industry with sales of $24.6 million.

Today, Mars Inc.'s annual sales are estimated at anywhere from $750 million to $2 billion (Business week says sales are in a range of $1.5-$2 billion). The firm, based in McLean, manufactures Snickers, Mars, Three Musketeers and M&M candies: Uncle Ben's rice and Kal Kan dog food, among other products. It has diverse manufacturing plants and holdings in this country, Britian, Australia and West Germany.

Control of the company passed in 1964 to Forrest Mars, a son of the founder, who formerly lived in a 615-acre estate near The Plains, Va., but now lives in Las Vegas.

According to a recent edition of Town & Country magazine, the 74-year old Forrest Mars is one of the richest men in America with a personal fortune estimated at between $300 million and $400 million. Business Week quotes an unidentified Mars vice president as estimating the Forrest Mars fortune in the billion-dollar league - which would put him in a class with the Rockefellers, Melons and du Ponts.

As has been the practice over many years, Mars spokesman Dean Musser declined yesterday to provide any information on his firm. Musser, who said he is the Mars counsel, declined earlier this year to identify the company's officers. In its annual survey of large area business, The Washington Post said the top executives of Mars were a "company secret."

James R. Fleming used to be chairman and A. Colin Baxter formerly was President and chief executive.There whereabouts are unknown, but Baxter had been viewed, as an interim Mars head until sons of Forrest Mars could take over. The sons, Forest Jr. and John, now work out of the McLean office and they apparently run the corporation. Both men live in Northern Virginia.

Advertising Age, in its annual survey, said Mars Inc. was ranked as the 71st largest U.S. advertiser in 1976 with outlays of $41 million for candy, rice and dog food ads (mostly television).

According to Business Week data, the heavy advertising has paid off: Mars now has more than 30 percent of the U.S. candy market, having replaced Hershey, which was in first place five years ago but which now is down to about 13 percent. Of the 10 leading chocolate candy bars sold, Mars has 5 - No. 1 Snickers, No. 3 M&M (peanut), No. 4 M&M (plain), No. 5 Three Musketeer and No. 6 Milky Way.

Financial consultants and securities analysts interviewed by The Post have described the closely-held Mars firm (the family owns all stock) as productivity-oriented and run by a small but effective management team. At one time, the company had a goal of 22 percent return on total assets - no more or less. Less would mean fewer profits and more would mean too little was spent on advertising and product improvements, Fortune magazine wrote in 1967.

Business Week estimates that Mars now earns profits equal to 6 percent of sales and 14 percent on investment - a range of $90 million to $120 million. The firm reportedly has a goal of 7 percent annual gains in profit and sales and one source said growth is 10 percent a year.

Mars is not without problems. Some of the firm's candy products have mentioned in petitions to the Federal Trade Commission, seeking agency action to limit candy advertising aimed at children.

Moreover, Business Week reports, Americans are eating less candy - per capita consumption has declined from 20.3 pounds in 1968 to 15.4 pounds last year. The McLean firm is responding to "what could be a calamitious trend" with a two-prong strategy of diversification into new food-related fields (Starburst is a new candy and the firm soon will offer cookies) and possibly other types of business, the magazine says.

A marketing executive, Howard Walker, recently was named to head the M&M/Mars domestic candy division in Hackettsotown, N.J., replacing a manufacturing specialist.