Rubbermaid has proved it's flexible.

''When people get married, that's good for our business, because when they set up housekeeping they'll buy new bathmats and things for their house,'' says Richard D. Gates, vice-president and treasurer of Rubbermaid Inc.

''And if people get divorced, that's good for our business, because they'll need to buy some things for two homes instead of one,'' he adds.

''If the economy is up, and people can afford to buy new houses, that's good for our business. And if the economy is down, and people can't afford to buy new houses, well, maybe they'll buy some of our products to fix up the home they're in.''

A bathmat here, a plastic wastebasket there, it all adds up - nearly half a billion dollars a year.

For the six months ending June 30, sales were $245.8 million, an 18 percent increase over the $207.9 million recorded in the first six months of 1983. Net earnings were $18.9 million, or $1.22 per share, up 19 percent from the $15.9 million or $1.03 per share of last year's first six months.

It was sales like these that pushed Rubbermaid into the Fortune 500 last year.

Rubbermaid makes things that just about everyone can use, such as plastic laundry baskets and turntables to hold spices in the kitchen cabinet. But it's made its mark by making high-quality versions of those everyday housewares, and thereby being able to command a higher price for them.

Rubbermaid has been, about as literally as possible, a household name since the depression, when the Wooster Rubber Company, which had made toy balloons, made its first rubber dustpans, hawked door to door in the evenings.

But the company's continuing success owes to its continual introduction of new products. ''Thirty percent of our sales come from products introduced in the last five years,'' Rubbermaid executives are wont to say.

New developments have been been coming especially thick and fast since 1980, when Stanley C. Gault took over as chairman and chief executive. Mr. Gault, a Wooster native and veteran of General Electric who had been in line for the top post there, has ''almost restructured the company,'' as Mr. Gates puts it.

But Gates says he doesn't want to give the impression ''that 'a sleeping giant has been awakened,' or anything like that. Rather, it's more as if the baton has been passed from one relay runner to the next.''

This view is generally endorsed by outside observers. But still, there have been some big changes. Rubbermaid dropped the line of food storage containers it had been marketing through the party plan, a la Tupperware; it also stopped making automobile floor mats.

There have also been some acquisitions - the Contact brand of decorative coverings, for one. These made a nice blend with Rubbermaid's existing shelf-paper line.

Industrial product lines - plastic pots for commercial agriculture, for example, have been enhanced, and the overseas marketing and sales forces have been beefed up.

This past April, Rubbermaid announced the acquisition of Little Tikes Inc., a privately held Ohio company making high-quality plastic toys and play furniture.

''Now this isn't the kind of thing you have to advertise on Saturday morning TV shows,'' says Mr. Gates, getting down onto the floor of his office to demonstrate Waffle Blocks, one of the Little Tikes products. ''This is the kind of thing parents and grandparents like to buy for their kids,'' he adds, fitting together the sturdy, brightly colored plastic blocks to make a makeshift wagon.

The Little Tikes acquisition, like that of Contact, has been seen as a good blend with existing Rubbermaid businesses. Some reservations have been expressed , however, that not all of chairman Gault's proposals for acquisitions have sat well with Rubbermaid's board.

And although Rubbermaid is widely hailed as a well-run company, one industry observer expresses what he calls ''a distant, vague concern'' that Mr. Gault's enthusiasm might end up pushing the company into some mistakes. ''He's such an enthusiastic salesman, and a dominant personality.''

But the same observer gives Gault credit for having built a good record in his tenure at Rubbermaid. ''Sometimes when someone comes from a big company to a (relatively) small one, you find it's their staff that's been carrying them. But he's shown that isn't the case here.''

Among this year's new products are the Servin' Saver food storage containers, intended to meet a market need for a top-quality product available through normal retail outlets, rather than time-consuming ''parties.'' Because of its streamlined distribution channels, Rubbermaid is expected to undercut the market leader, Tupperware, by one-third on price.

Indeed, despite Rubbermaid's image as a high-quality and (relatively) high-price producer, the observer quoted above suggests, ''They must be the low-cost producer.'' Plastic pellets arrive at the plant here by tank car and then swoosh through the plant in overhead pipes that lead to injection molding machines. The jaws of these machines pop open every few seconds to drop out an ice cube tray or other product onto a conveyor belt.

This observer's implication is that sales of the old reliable items help finance the development of new products, such as the new lines of microwave cookware. Company research had identified three levels of expertise among owners of microwave ovens - the uncertain beginner, the adventurous user, and the confident microwave cook. The company went for the ''confident'' group first, introducing a top-quality product made of Micrel in January of 1983. This past April the ''Heatables'' and ''Cookables'' lines came out, for the beginner doing mostly reheating and for the adventurous user, respectively.