RICHMOND -- First there was the aluminum can. Then came the plastic bottle. Now Reynolds Metals Co. is getting ready to introduce a hybrid resealable aluminum can that executives of the company hope will be the biggest thing to hit the highly competitive soft-drink container field since the pop-top.

Reynolds says the Reylock can has the lightness and convenience of aluminum cans, with the resealability of plastic or glass bottles. And unlike plastic bottles, it will be recyclable.

The Reylock can will be introduced to soft-drink company executives at a trade show in Chicago this week. Reynolds officials decline to estimate the potential sales of the resealable can, but they call it one of the biggest developments in the Richmond-based company's history.

"The best possible case is that the thing goes crazy," said Lee R. Gunton, national marketing manager for the Reynolds can division. "At the worst, this will be a nice package for somebody."

"The Reylock can represents the first totally recyclable large beverage container over 12 ounces specifically designed for the soft-drink market," said Robert D. O'Donnell, can division chief.

Because the container can be opened and resealed repeatedly, it will allow buyers to consume beverages over extended periods.

O'Donnell said the new product offers as much business potential to Reynolds as the stay-on pull-top tab, which it developed and patented in the 1970s. The company continues to profit, either directly or through royalty arrangements, every time a top is popped. Packaging and containers accounted for 43 percent of Reynolds' 1986 sales of $3.6 billion.

The Reylock will come in six sizes: 16-ounce, half-liter, 24-ounce, three-quarter liter, 32-ounce and one liter. It will not come in smaller sizes, since such drinks usually are consumed in one sitting.

Designed with soft-drink makers in mind, the can may be used for any drink from mineral water to fruit juices to isotonics, such as Gatorade.

The Reylock is an aluminum cylinder sealed completely at the bottom. The top is a small inverted cone with a hole in the center and a plastic seal.

To open, a user lifts the seal's two handles and pulls it off. To close, the user snaps the top into the hole and forces the handles down with the palm. The can also can carry a tamper-resistant seal.

The company plans to have the new can in a test market with at least one commerical customer by the end of this year, O'Donnell said. If consumers accept the can, Reynolds will begin full production next year. By the end of 1988, the Reylock could appear in grocery stores across the country.

Reynolds' search for such a new product began in 1982, when "we decided that the aluminum can had started to mature in the single-serving market, and we looked for a way to go after the larger sizes," O'Donnell said. "The result of that effort is our resealable can. We spent as much as five to six man-years per year over the last five years bringing this to the marketplace."

The stay-on-tab took two years to develop.

Reynolds does not intend to license Reylock can production in the immediate future, choosing instead to make the product itself.

Reynolds officials are cautious about predicting how big a hit the can could be, but O'Donnell said that if it takes off, Reylock could take as much as five years to become a major item in the container business.

"Next year in the first quarter we will find out what the consumer acceptance is in the store and that obviously will tell us how big a winner we have," O'Donnell said.

"We don't see any economical problems. We don't see any recyclable problems. And we see many, many advantages. So we're very positive," he said. "The final answer will be after we see how many housewives buy it and how often they buy it."