Modern technology and a return to often-criticized 19th century labor practices are sending millions of people into the world of work without leaving their homes.

Their products and services run the gamut of the marketplace, from mittens sewn by newly arrived immigrants to the newspaper pieces syndicated columnist Art Buchwald taps out on his home computer.For at least 8 million Americans, and possibly many more, the journey to work consists of walking from one part of their house to another. No arduous commute in rush-hour traffic for them. No need for baby sitters. No boss looking over their shoulders. And for those who operate businesses, no expense for rent, utilities and other overhead.

But working at home has its drawbacks. Many home workers receive low wages and no fringe benefits. Many are in technical violation of zoning laws that bar commercial endeavors in residential neighborhoods. The federal Fair Labor Standards Act prohibits unsafe working conditions, sub-minimum wages and the employment of children, but it is difficult if not impossible to enforce in the home.

Driving the trend toward working at home is the personal computer, which is used increasingly by clerical workers to do tasks formerly performed in offices, as well as by home-based entrepreneurs.

"People are finding they can merge nicely their careers and their home situations," said Deputy Labor Secretary Dennis E. Whitfield. "People coming out of school know they have some options."

Buchwald began writing his newspaper column at home in the 1970s and today comes to his downtown Washington office for a few hours in the mornings to read the mail and "just get out of the house."

"You feel out of it if you don't have some place to go in the morning," Buchwald said. "The most dangerous thing about working at home is that the husband and wife are around each other all day. Unless there's a pretty good relationship, it's hard for two people to be around each other constantly."

Another category of home work is in apparel and related industries. This dates to the early days of the Industrial Revolution, when long hours, substandard wages, the exploitation of child labor and unhealthy working conditions eventually led to state and federal restrictions on industrial home work.

But in one of its last major deregulatory acts, the Reagan administration repealed federal bans on homework in five industries - gloves and mittens, embroideries, buttons and buckles, handkerchiefs and some jewelry production. The restrictions, which had been adopted in the 1940s, came off the books 11 days before Reagan left office.

A third category of home workers are professionals and others with a tradition of operating out of their homes. These include doctors, dentists, veterinarians, accountants, artists, writers, beauticians, sales people, caterers and consultants.

The U.S. Bureau of Labor Statistics estimates that 18.1 million people work full or part-time at home. But if farm employees and those working less than eight hours a week are excluded, the size of the home-based workforce drops to 8.3 million. Of these, about 950,000 are considered to be employed fulltime.

Private groups place the size much higher, however. LINK Resources Corp., a New York marketing firm, said 24.9 million persons worked full or parttime at home last year, while Fuji Photo Film USA Inc., a computer supplier, placed the total at 34 million.

The American Home Business Association estimates there are 13 million home-based businesses with an economic impact of $100 billion.

According to the Bureau of Labor Statistics survey, service jobs - such as doctors, repair shops and child care providers - made up about half of the 8.3 million home-based workers.

Working at home is particularly attractive to retired people, according to bureau economist Francis W. Horvath. Persons over 55 account for 12 percent of total jobs in the United States, but nearly 20 percent of home-based employment.

Computers appear to play a major role in the growth of home-based work, but there are no reliable estimates of the number of persons who "telecommute" to their offices via computer modems. However, Fuji's marketing analysis found the home office is the fastest-growing segment of the personal computer market.

No studies have been carried out on how productivity is affected when computer terminal work is performed at home. But at the half-way point of a two-year pilot study in California, the feedback from both supervisors and employees has been positive, according to David Fleming, director of the state office of telecommunications.

Between 150 and 250 state employees ranging from data entry clerks to administrative law judges are working at computer terminals in their homes, while others operate from neighborhood offices. The purpose, Fleming said, is to compare their absenteeism, turnover and effectiveness with control groups of employees working in conventional settings.

Also to be gauged are the potential benefits from reduced traffic congestion, energy consumption and improved air quality if home-based work is applied throughout state government, he said.

Joanne H. Pratte of Dallas, a consultant to the project and an authority on the home office market, said all kinds of tasks can be performed with home computer terminals, particularly jobs where concentration and an interruption-free environment are important.

Norman Bodek, head of the Data Entry Management Association of Norwalk, Conn., said a big advantage of working at home for young mothers is that they are able to care for their children while earning a paycheck.

But Fleming said that in the California experiment, parents are urged to hire babysitters or make other arrangements rather than try to juggle their work loads and child care simultaneously.

Pratte and Bodek said many home-based workers and entrepreneurs toil in violation of zoning laws. "But across the country there is some recognition that home business is going on and there is an unstated policy of not enforcing the laws unless neighbors complain," Pratte said.

Bodek said most laws barring business operations in residential neighborhoods date to an era when blacksmiths and other tradesmen would create excessive noise, dirt and smoke in such settings. "Somehow the doctors and dentists and lawyers were excluded from these zoning laws," he said.

The Labor Department's decision to repeal restrictions on industrial homework in the garment industry sprang from the deregulatory climate of the Reagan years and not because the industry lobbied for it.