Consumer activist Ralph Nader yesterday asked President Reagan to abolish the White House Office of Consumer Affairs, calling the office a fraud and a waste of money.

In a nine-page letter to Reagan, Nader said that the head of the office, Virginia Knauer, has no clout and is satisfied with "a vacuous public relations role." He described a number of issues, from auto safety standards to the labeling of mechanically deboned meat, in which he said Knauer's office has failed to be a voice for consumers.

Other consumer groups also have been critical of Knauer, but they declined yesterday to join Nader's call to kill the office.

"Institutionally, it's important to have a consumer affairs office in the White House," said David Greenberg, legislative director for the Consumer Federation of America. He said, however, that Knauer's "voice has been largely silent of late."

Joe Dawson, a spokesman for Knauer, said the office was accustomed to attacks from Nader. "We get a letter like this from Nader about every four months," he said. "We're kind of used to it . . . . We're not taking it too seriously. In fact, it's given us all a morale boost."

During the Carter administration, when the office was run by Esther Peterson, it had a staff of about 50, a budget of nearly $2 million and represented consumers in some public utility rate-making cases.

Nader charged in his letter that, since Reagan took office, the budget and staff have dwindled and Knauer, who was White House consumer adviser under presidents Nixon and Ford, has been content to ask industry to voluntarily aid consumers.

He said that after Knauer's one attempt to speak for consumers last December "she was contradicted so severely she has remained quiet ever since." Knauer wrote a letter to Congress endorsing a Federal Trade Commission rule that would have required used car dealers to disclose known defects to buyers.

A few days later, an official at the Office of Management and Budget said the administration opposed the rule as a serious paperwork burden on small businessmen. The OMB official said Knauer's views were her own, not the administration's.

Nader concluded that Knauer's office "is unwilling to do anything for the American people and is a waste of the taxpayers' money. It should be abolished."

He said that the existence of the consumer office "only misleads citizens into thinking that they have an ear in the White House, into believing that someone is watching out for their rights. Since this is assuredly not the case, spare Americans the pretense and the useless expense of their funds by closing this office down."

Mark Silbergeld, Washington director of Consumers Union, which publishes Consumer Reports, said he wouldn't endorse Nader's proposal, although he agreed that Knauer's office has become ineffective. "Most consumer groups have written her office off as irrelevant and having no influence in this adminisitration."

He suggested that, instead of abolishing the office, "they put a sign on the door saying 'Four-Year Vacation.' "

Dawson acknowledged that there have been budget and staff cuts at the office, but "we have to take our share in this time of austerity."

He added that he had no quarrel with Nader's characterization in the letter that Knauer depended on voluntary cooperation with industry to help consumers. "We've got things going that Ralph Nader would never get going," he said.

Dawson cited a recent announcement by the Del Monte Corp. that it would include salt content on labels for its products. Knauer testified in favor of the idea last year, Dawson said, but advocated voluntary industry action, rather than government requirements.

He also said the office is working now on "several approaches we think the public will find useful" in settling alleged overcharges on gasoline and fuel oil made by major oil companies during federal pricing regulations.