The broad greenswards of suburbia are proving to be fertile ground for a new service business. Mowing lawns has remained the province of teenage entrepreneurs, but hundreds of companies have sprung up in the past 10 years to provide fertilizer and pesticide treatment for lawns.

Similar services have long been available at high cost from landscapers. In recent years, however, the two-career suburban family -- pinched for leisure time -- has created a sizable middle-class market for lawn care services, a market that, by one estimate, will reach $2 billion this year.

Most of that is spread among very small companies, averaging $200,000 to $300,000 in annual revenues, according to James R. Brooks, executive director of the Professional Lawn Care Association of America, a 500-member industry group. But one company, Spring-Green Lawn Care Corp. of Naperville, Ill., has built a healthy franchise business out of it, with some 62 franchisees throughout seven midwestern states. Starting in 1977, with one customized spray truck operating out of a warehouse, William R. Fischer, Richard G. Gretz, and Thomas Hofer have built Spring-Green into a $63-million business, tending 50,000 yards. The company plans to open 15 to 20 new franchises this year, expanding from the Midwest into Pennsylvania, Delaware, and New Jersey.

One reason for consumers' attraction to professional lawn care service, says Brooks, is fear about potential dangers of toxic pesticides. The growing concern about chemical hazards has prompted many homeowners to hire a professional to handle chemicals when they are needed.

Convenience, though, appears to be the greatest attraction to lawn care companies. Kent and Barbara Lluffy, who have three children, bought lawn care service for their home in Aurora, Ill., for just that reason. "Basically, my husband is lazy when it comes to taking care of the yard," Barbara Duffy says with a laugh. But, she adds, "Sometimes he comes home from his insulation company and likes to play tennis. All the yards around us are gorgeous. So we wanted to make sure we got the right fertilizer and the right care."

What's more, says Kent Duffy, the service is relatively cheap. Indeed, because of high volume -- one Spring-Green truck can service 20 to 30 lawns per day -- Fischer maintains that his company's service costs homeowners the same as if they did it themselves. A customer pays about $130 for four to five Spring-Green applications of fertilizer, weed control, and insect control in one year. For $100 Spring-Green will provide four treatments of tree and shrub root fertilizer and insect controls.

As Spring-Green attracts consumers with low-priced services, it is stepping up its marketing effort. "Marketing is the cornerstone of any successful business, and lawn care is certainly no different," says Fischer, who has a BS degree in ornamental horticulture from the University of Illinois.

Using a four-color brochure that emphasizes guaranteed quality service and convenience, Spring-Green's direct-mail campaign is reaching more than 3 million consumers, aiming at households with incomes of $22,000 or more.

The company estimates that of 52 million home-owned yards in the United States, 20 million of them are owned by families with incomes of $22,500 and up. Of those families, only 2 to 3 million use lawn care Says Fischer, "We have a long way to go."