If Cabbage Patch Kids were the toys to have last Christmas, then this year's hot holiday item is Hasbro's Transformers. But if you haven't got yours stashed away in your closets, then your kids -- who undoubtedly see every Transformers commercial that appears on television -- may be disappointed.

They are very hard to come by.

When Lowen's toy store in Bethesda opened for business Saturday, an estimated 80 people were lined up at the door to buy the latest shipment of Transformers -- those toys that change from cars or airplanes to robots and back. One woman bought $400 worth of the Transformers. And within three hours, the store had sold its entire stock of 502 Transformers.

"We just can't get enough of them," said Lowen's toy buyer John Hall.

Other area toy store officials yesterday reported the same problem. "We have them on and off," said Richard Sponaugle, manager of Juvenile Sales in Alexandria. Yesterday he didn't have any and wasn't sure when the next supply would arrive. "We are trying from every source available to us," he said. "But we expect them when we see them coming through the door."

Sponaugle said his store was fielding about 100 calls a day from anxious shoppers asking when more Transformers might arrive.

Bargain Town in Northwest Washington had "a few" Transformers yesterday. "But you'd better hurry, because they go fast," the clerk advised one telephone caller.

Meantime, the television commercials promoting Transformers keep on running -- along with a weekly syndicated children's television show in which the characters are Transformers.

That combination has increased demand for Transformers toys and frustration for children and parents, according to Ann Brown, chairman of the group that conducts an annual toy survey for the Americans for Democratic Action.

"For the child, these huge advertising campaigns build expectations for toys that can't be fulfilled when parents can't get the toys," she said. "And for the parent, it takes some of the joy out of Christmas, because it makes shopping such a burden, when you have such lines and when the toy they want isn't available."

Brown described the Transformers television show as "merely a long advertisement."

Hasbro Bradley Inc., which is based in Pawtucket, R.I., makes more than 25 different kinds of Transformers, ranging in price from $3 to $30. The small, three-inch car Transformers are the least expensive; the larger 18-inch airplanes cost the most. In between are various sizes of other cars, planes, guns and tape players -- all of which convert into something else -- typically, a robot.

Stephen Schwartz, Hasbro's senior vice president of marketing, said the company would "love to ship more goods." But, he said, "when a phenomenon hits, there is no way to catch it in the first year."

He said that Hasbro would cancel the TV commercials that are scheduled to appear between now and Christmas if it were possible to do so. "But we make commitments to television very early and once we buy it, that is it," he said.

Commercial time for Transformers for the 1984 season was purchased in March, Schwartz said, before Hasbro realized the size of the demand for the toys.

At present the Transformers are featured in eight to 20 commercials a week, Schwartz said. He said Hasbro sold the idea for the television Transformers program to another company and has no control over its distribution.

"The last thing we want is an unhappy consumer," he said.

"But this is the age of shortages in the toy business," said Schwartz, who said that he also has been a victim of demand exceeding supply. "My kids wanted Cabbage Patch dolls. I couldn't get them. They wanted Trivial Pursuit. I couldn't get it either."