The Carter administration moved swiftly yesterday to impale Ronald Reagan on a purported misstatement about federal regulation of the auto industry, just as it also did recently when he made alleged misstatements about the Ku Klux Klan and about relations with Taiwan.

He is "filling the air with misstatements, half-truths, or twin positions," Secretary of Transportation Neil Goldschmidt told an afternoon news conference. "Or to say it another way, his mouth was in gear -- but his brain was still in idle."

His harsh attack -- cleared at the White House -- was triggered by Reagan's Tuesday pledge that as president he would try to get rid of "several thousand of what I think are unnecessary regulations" on U.S. automakers and would act to halt the "deluge" of Japanene imported cars.

Campaigning in recession-ridden Detroit, the Republican candidate told employes of Chrysler Corp. that "regulations . . . have caused your problems. eWe'll give regulation a major overhaul, and prove you don't have to lay people off to have clean air, safe cars and good fuel economy."

Disputing Reagan's "several thousand," DOT told reporters that the number of regulations affecting motor vehicle safety is 48 and the number dealing with fuel economy is two. At the Environmental Protection Agency, Mike Walsh, who heads EPA's motor vehicle program, put the number of regulations affecting air purity "in the range of 12 to 24."

Goldschmidt's prepared statement listed no numbers, but, in reply to questions, he estimated that the auto safety rules -- which, like others, apply to imported as well as domestic cars -- totaled 50.

Also in response to questions, the secretary said that White House chief of staff Jack Watson had said it was "acceptable" for him and other Cabinet members to call "factually inaccurate" statements to public attention.

For Reagan to say several thousand needless regulations are to blame for massive unemployment and sales losses in Detroit "is both irresponsible and factually untrue," Goldschmidt said. He added:

"As usual, Gov. Reagan misses the main point, one which the auto industry itself acknowledged in its first meeting with the president. If we get rid of every single regulation that affects the auto industry . . . it would not make the auto industry well."

Moreover, Goldschmidt charged, Reagan's proposal is irresponsible because it would lead to "the undoing" of laws on occupant safety and clean air.

He recalled that Reagan, while governor of California, said his state's clean air standards, the toughest in the nation, were "absolutely necessary requirements."

"It is also absolutely untrue and it is factually inaccurate in every sense to try to lay at the door of fuel economy regulations set by Congress and this agency the current problems of the auto industry," Goldschmidt said.

"The fuel economy standards . . . are the reason, in large measure, that there was a K-car plant for Ronald Reagan to visit yesterday," he added. The K-car is Chrysler's new fuel-efficient compact, and its hope for a return to economic health.

Asserting that consumer demand for fuel economy became long ago more exacting than congressionally mandated regulations, Goldschmidt said history shows that the standards "were the reasons that the automobile companies in the United States . . . got going producing and developing fuel-efficient cars."

The secretary characterized Reagan's statements on trade restraints and the government loan guarantee for Chrysler as "acrobatics."

On May 15, Reagan, during an earlier visit to Detroit, said, "Trade protectionism is not the answer." On Tuesday, Goldschmidt said, Reagan, "working another side of the street," said he favored the Japanese restraining their exports "one way or another."

As to Chrysler, Reagan said last October, "What's wrong with bankruptcy?" On Tuesday, while acknowledging his original opposition to the bailout, Reagan endorsed it.