National Consumers' Week, an event designed to focus attention on the consumer's importance in the marketplace and the economy, got off to a wet and somewhat controversial start yesterday on the Mall where more than four dozen exhibitors at a consumer "fair" waited inside their tents for the rain to stop and the crowds to come.

Hardly anyone showed up and the rain barely slowed down during most of the day.

"It's a disaster--the only people we have seen so far are other exhibitors," said Shawn Hausman, one of the two women in charge of the display and literature for the American Council of Life Insurance.

Among those who did attend the fair was Nancy Drabble, director of Public Citizen's Congress Watch, an activist consumer group that complained many of the fair's exhibitors were anticonsumer corporate trade associations. Among those she cited were the National Automobile Dealers Association, which has fought a government rule requiring used car dealers to disclose defects in cars they sell, and the American Council of Life Insurance, which has opposed disclosure laws on the rate of return on whole life insurance.

"This is like proclaiming National Pest Control Week and inviting the cockroaches as honored guests," Drabble said.

Her comments were promptly dismissed as "ridiculous" by Virginia H. Knauer, special assistant to the president and director of the U.S. Office of Consumer Affairs, which is coordinating the week's activities with representatives of other groups.

"I wish they Congress Watch would be constructive for a change," Knauer said during a tour of the exhibits set up in three tents on the Mall near Constitution Avenue and 14th Street.

Knauer said that some other consumer groups are supporting Consumer Week and participating in its events. She singled out Consumers Union, the publisher of the magazine Consumer Reports, which had a representative at the fair to explain its product-testing procedures. The Consumer Federation of America also is taking part in the week's activities, she said.

Knauer also downplayed the fact that the consumer fair featured some government agencies such as the Federal Trade Commission and the Consumer Product Safety Commission that the Reagan administration has vigorously sought to dismantle or reduce in scope.

And as for the fair's promotion of programs that are being discontinued, such as government consumer publications, Knauer said simply that the publication cutbacks are "marginal."

One of the publications is "The Car Book," a highly praised booklet put out by the National Highway Safety Transportation Administration. "The Car Book" was prominently positioned on that agency's display table at yesterday's fair. But an agency official said that "The Car Book" won't be reissued when the supply has been distributed.

Knauer and other sponsors of National Consumers' Week say they hope that the activities, which involve everything from boat safety to home repairs, will lead to sustained consumer education efforts. The need for such efforts has been documented, they said, by surveys showing that many consumers are deficient in basic skills.