In a world where people become impatient waiting for a fax to go through or a microwave oven to beep, few are willing to spend 20 minutes assembling a cake, let alone the hours involved in making bread.

A science skillfully practiced by the ancient Egyptians is slowly becoming a dying art at home.Only 20 percent of all adults in the United States baked at least once in 1994 as a leisure activity, down from 22 percent in 1985, according to Mediamark Research Inc. of New York City.

Because of the lack of interest, there has been negligible growth of the home-baking market. David A. Weiss, president of Packaged Facts, a research company in New York, said that in 1993 there was a minuscule .3 percent increase in home-baking products from the previous year, with sales reaching $3.2 billion. By contrast, retail bakery sales in the United States were estimated at more than $7 billion in 1994.

An invitation to participate in a New York Times home-baking questionnaire posted on America Online's popular "Cooking Club" bulletin board received only one response, from Betsy Stout-Jones. She said by e-mail that she used to bake a few times a week but has had to cut back to at most once a week. "My career took over my life," said Stout-Jones, the promotion director for WMXQ-FM and WAPI-AM radio stations in Birmingham, Ala. "It's more of a luxury now, but if I had my way, I'd bake every day."

Today, many people think the term "baking by scratch" means opening a box of mix. And because of consumer impatience and a lack of baking skills, manufacturers are making the mixes even easier to use. Last year, Pillsbury introduced one-step, just-add-water angel food cake and brownie mixes, and they have been popular. This spring, the company will introduceseveral other time-saving products, including reduced-fat biscuit dough and chocolate-chip cookie dough.

Pam Becker, a spokeswoman for General Mills, maker of Betty Crocker products, said that sales of all-purpose flour had been slipping for a number of years and, surprisingly, microwave mixes never proved popular. The best sellers, she said, are no-bake desserts, which are finished in the refrigerator instead of the oven.

For those intimidated by every aspect of baking, some new mixes from Duncan Hines don't even require greasing a pan.

The presence of women in the work force has contributed to the decline of baking as a hobby. (The majority of home bakers are women.) At the start of World War I, half of all American women had at least five children and spent an average of five hours in the kitchen each day, Irena Chalmers wrote in "The Great Food Almanac" (Collins Publishers, 1994). Women today have an average of two children and spend about 15 minutes just preparing dinner.

On a recent Saturday morning in the well-stocked baking aisle of an A&P in Fort Lee, N.J., more than 100 people cruised past in half an hour. Of those, only 12 stopped to buy baking products; eight of them bought mixes. All 12 lamented that they would love to bake more but had little time. "I can't even find an opportunity to do my laundry - forget about making a cake," said one woman as she read the instructions on the back of a two-step cake mix. She put the box back on the shelf and headed for the frozen pies.

Also working against home baking is the rise in the number of bakeries in supermarkets and elsewhere. These bakeries are providing convenience and variety, and the best ones offer elaborate goods that even an accomplished home baker might have difficulty creating.

Joy Taylor, the senior food editor at Better Homes and Gardens magazine, said that her 7.6 million readers had less knowledge about baking than preceding generations. "It's a shame," she said, "because techniques and recipes are not being passed down through the generations. People's heritages are being lost."

The skills are not being taught outside of the home, either. "Few take home economics or 4-H classes anymore," said Sharon Maasdam, a home economist for The Oregonian newspaper in Portland.

A lack of technical proficiency was recorded by Land O'Lakes Holiday Bakeline, which received a record-breaking 40,000 calls from Nov. 1 through Dec. 24 last year. (More baking is done between Thanksgiving and Christmas than at any other time of the year.) The most common question was how to prevent cookies from spreading when baked on a cookie sheet.

The only real growth in the home-baking industry seems to be in bread-baking machines, which do everything but butter the bread. They were introduced less than a decade ago and are now in 7 percent of the households in the United States.