SUFFOLK, VA. -- With a major expansion in progress at its plant here, Hills Bros. Coffee Co. has some big ideas about altering its demitasse image.

"The biggest thing we needed to overcome here was just a general lack of coffee knowledge," said Charles Cortellini, manager of the plant.

When he junked plans for veterinary school to take a management position with Hills Bros. 14 years ago, he reassured his mother by telling her the company was the third-biggest coffee roaster in the country.

But he didn't tell his mother that Nos. 1 and 2 in the business had a combined 60 percent of the market compared with Hills Bros.'s 7 percent share.

Hills Bros. remains No. 3, trailing Maxwell House and Folgers. But Cortellini's company has nearly doubled its share of the domestic coffee market since 1976.

"They literally have been sneaking up on the two giants," said Richard Hanley, editor of World Coffee & Tea magazine.

In early 1988, Hills Bros. opened its new manufacturing plant in Suffolk's Industrial Park. Shortly afterward, the company's top officials flew in from their San Francisco headquarters to announce they would expand the plant's production capacity tenfold, to some 150 million pounds of coffee annually.

When the second phase brews into operation by early 1991, Hills Bros. will have spent $35 million on the Suffolk operation. The plant will be the largest in Hills Bros.' six-factory network and the most automated of its kind in the world.

Earlier in June, Hills Bros.'s parent, the Swiss-based Nestle S.A., said the company had done well enough to be given the management of Nestle's other domestic coffee brands, Nescafe and Taster's Choice.

As Tom Pirko, president of Bevmark Inc., a Los Angeles-based beverage-industry consulting company, said, "There's no question that the third leg on this stool ... is the one to watch."