Teflon and nylon, the two products that began a materials revolution that touched everything from women's legs to frying pans, turn 50 this year.

Both emerged from the laboratories of Delaware's E.I. du Pont de Nemours Co. in 1938, and this week Du Pont kicks off a lavish birthday celebration for its two most famous inventions.

Teflon, the world's slipperiest man-made substance, which eventually would coat the Pontiac Silverdome and label a presidency, and Nylon, which almost singlehandedly turned Du Pont into one of the world's largest corporations, will be the subject of year of hoopla. It will begin with a special presentation at the National Press Club in Washington beamed live to Toronto, Paris, and London, and a fashion show at the Willard Hotel.

The anniversary, however, is hardly an exercise in nostalgia. Nylon -- and to lesser extent Teflon -- is still very much at the center of the Du Pont empire.

"If you were to take out of Du Pont all the business we have today that is derived from nylon, you'd make a Fortune 500 company," said Alexander MacLachlan, the company's senior vice president of technology. "Remember, that's after 50 years. It's that important to us."

Last year the company racked up sales of $27 billion, and two-thirds of that follows the nylon trail blazed in advanced materials half a century ago. The building where nylon was invented is still in use at the huge "experimental station" the company maintains on a former country club outside Wilmington.

Indeed, as the company prepares for aggressive diversification over the next decade into electronics, biotechnology, and pharmaceuticals, the challenge it faces is very much a reflection of Du Pont's formative experience with nylon 50 years ago.

Nylon was invented at Du Pont under a special "fundamental research" program set up in the 1920s by Du pont executive Charles Stine.

Stine argued that pure scientific work of the type typically done in universities "is bound to result in the discovery of new highly useful and in some cases indispensable knowledge." In 1928 he hired Wallace Carothers, a brilliant Harvard scientist, with the promise that he would have the freedom to pursue his interests in theoretical organic chemistry.

Out of that creative freedom, 10 years later, came Carothers' discovery of nylon -- and a lesson that the company never forgot.

"We still lure people here with those same promises," said Richard K. Quisenberry, heir to the program started 60 years ago by Stine. Today almost 10 percent of the $1 billion a year Du Pont spends on R&D is given over to pure scientific research. Some 65 scientists from various universities are currently conducting research at Du pont facilities, and last year Charles Pedersen, a retired Du Pont scientist, won a Nobel Prize for chemistry for his work at the Du Pont experimental station during the 1960s.

"Their research capacity is as good or better than anyone else in the world," said Leonard Bogner, a chemical industry analyst with Prudential-Bache Securities. "If Du Pont sets their mind on inventing something, they'll do it."

The key to the Du Pont research program is patience, a willingness to spend enormous amounts of money on research before realizing any gain. "Nylon sounds like it was developed quickly, but it wasn't. It was a tough go. We make a lot of money off things that take 20 years to straighten out," said MacLachlan. "The strength of a big company like ours is to stick with something that doesn't create value all that fast."

But once a product reaches the market, expectations are high. "They've got a home-run philosophy," said Firoze Katrak, vice president of Charles River Associates in Boston. "They're not looking to get on first base. They're after big opportunities with big payoffs," Katrak said.

That was certainly the case with nylon, which during a half-century run has earned the company in excess of $10 billion. Carothers wasn't intending to produce a new fiber, but one day in 1930 one of his associates stuck a glass rod into a test tube of molten polyester and pulled out a stringy mass that stretched like a fiber when it cooled. That wasn't nylon, but it was the beginning of an exciting chase that ended eight years later with a product hailed as the first synthetic silk.

The first nylon products were toothbrush bristles, fishing line and surgical suture. But when Du Pont realized the product's potential in women's hosiery, nylon became a sensation. During the World War II, Betty Grable auctioned her nylon hose at a war bond rally for $40,000. In San Francisco, 10,000 stocking-hungry people packed Market Square, where a department store was holding one of the first nylon sales in the area.

Teflon's discovery didn't quite kick up the same fuss. Discovered by accident when Roy Plunkeet, a Du Pont scientist, saw a supposedly empty metal cylinder lined with a white, waxy substance, Teflon was classified during the war by the Pentagon -- which used it for the top-secret Manhattan project -- and only became a household name in the 1960s with the release of Teflon cookware.

After 500 million pots and pans, Teflon is still going strong. Du Pont combined Teflon with nylon to make its hugely successful Stainmaster carpet, which -- after little more than a year in the market -- has already produced hundreds of millions of dollars in sales.

Recently, however, the corporate philosophy that produced nylon and Teflon has come under fire. One of Du Pont's most recent miracle products was Kevlar, a lightweight high-tech fiber five times stronger than steel. But for a long time Kevlar was a product without a market.

Originally developed to be the major ingredient in auto tires, tire makers rejected it as too expensive. Today, after 25 years of development, $700 million in capital expenditures and an estimated $200 million in losses, Kevlar has just reached the break-even point. And with Kevlar patents due to expire in 1990, the company admits that sales will probably level off well below original expectations.

"Kevlar was supposed to be a home run," said Katrak. But it wasn't, and the experience has led Du Pont to reconsider the company's basic attitudes.

Company executives now speak of reversing the traditional Du Pont research-and-development approach of finding markets for its discoveries. Now it is taking aim first at markets and seeking products to fill them."Marketing Excellence: A Du Pont Priority." According to Bogner: "They're moving from a product-driven to a market-driven philosophy."

For some analysts, the recent changes in Du pont are a cause for optimism. But others worry that they bespeak a worrisome new impatience at the company, an emphasis on short-term profitability at the expense of the company's traditional commitment to long-term research.

Perhaps a more serious challenge to the Du Pont way comes from the company's recent foray into the high-tech fields of biotechnology and electronics, where the technology cycles are shorter, competition from smaller firms is stiffer, and Du Pont's traditional advantages of patience and size are often more an impediment than a virtue.

"It's a marvelous company," said Ralph Hardy, who headed Du Pont's life science program for five years before leaving to join the small Boston-based biotechnology company Biotechnica International Inc. in 1984. "But there's an intensity in a small company that you don't see at a large corporation like that. In a small company, most employees are participants, and there's nothing like that to bring out the best in an individual... . In terms of decision-making and getting agreement, I can do more in a day at Biotechnica than I could in a month at Du Pont."

MacLachlan admits that is a concern. "Small companies tend to be a little faster on their feet. They get into the market faster, they have a tendency to be more driven." Du Pont, he said, sometimes is guilty of dragging its feet and sticking with unfruitful research projects too long.

But Du Pont officials insist that the company is becoming more flexible, pointing as an example to the Genesis 2000 DNA gene sequencer introduced last fall. The desk-top machine, which cuts the time needed to decipher the biological structure of genes from a matter of months to an afternoon, was created through an unusual collaboration among groups of scientists at the experimental station doing unrelated work.

Working together informally, scientists from the various departments conceived the idea on paper 2 1/2 years ago, and quickly carried the project forward to the point where Du Pont now stands with a very competitive entry in a $100 million-a-year market.

"The whole thing was done sub rosa," said MacLachlan. "No one managed it except the people who actually did it."

Added Quisenberry: "The success of the development thus far has been the close coupling of science in all the departments and the good sense of management to stay out of the way."

To encourage that kind of spontaneity, Du Pont has since 1979 had a number of special technology committees, drawing together representatives from various departments to promote flexibility and cross-fertilization of ideas.

"I can't tell you it worked very well in the beginning," MacLachlan said. "You don't take people who are used to being independent and say 'Now you've got to work together.' But as time goes on you get a culture change... . Now we have a mechanism in place that forces us to work together."

Will it work? Some analysts still fault the company's efforts in pharmaceuticals and biotechnology for taking too long to come up with marketable products. "At this stage all their efforts in the biomedical area have yet to bear fruit. If they keep doing things as they have so far, they'll have a long way to go," said William R. Young, an analyst with Drexel Burnham Lambert Inc. in New York.

But few doubt that the Du Pont will find a way to adapt its corporate culture to the challenges of new technologies.

"When people ask me who I worry about at night, I tell them I worry about companies like Du Pont," said Jerry Caulder, president of Mycogen, a California company that, like Du Pont, is engaged in developing agricultural chemicals through biotechnology. "Their only real weakness is that they take longer to make decisions. But once they decide to get into an area, they've got the patience, the money, and the direction."