Ronald Reagan said yesterday that a rapid U.S. arms buildup would be good for the United States because it would strain the defense-burdened Soviet economy and force the Soviets to the arms control bargaining table.

"The very fact that we would start would serve a notice on the Soviet Union," Reagan said during a two hour meeting with editors and reporters of The Washington Post. ". . . I think there's every indication and every reason to believe that the Soviet Union cannot increase its production of arms . . . They've diverted so much to military that they can't provide for the consumer needs. So as far as an arms race is concerned, there's one going on right now but there's only one side racing."

Reagan stressed his committment to nuclear arms negotiations with the Soviets, if they want to negotiate actual reduction of arms. This has become a familiar message from the former California governor as he tours the East, meeting publishers and politicans and trying to convince skeptics and supporters alike that he is a reasonable man who would make a reasonable president.

The Reagan road show moves to Capitol Hill today, where Sen. Paul Laxalt (R-Nev.) will unveil a series of congressional task forces aimed at providing Reagan with instant answers to difficult questions.

In his interview yesterday, Reagan said he favored a constitutional amendment limiting federal government spending to a percentage of the gross national product. He suggested that the right figure might be 19 percent, with escape clauses for wars or other emergencies.

Reagan said he favored an amendment because it couldn't be changed at the whim of Congress. But he said he would settle for a law in the interim because it would take a long time to ratify an amendment.

This was a slight in Reagan's position. In a policy statement issued Jan. 21, Reagan said he would prefer a law but would also support a constitutional amendment.

Reagan said he had not decided whether it was necessary for the United States to have nuclear arms superiority over the Soviet Union or whether parity would be sufficient.

"It would be safer that way [with superiority]," Reagan said, "but maybe it wouldn't be necessary. I"ve got an open mind."

Reagan said he saw no conflict of interest in the fact that a public relations firm headed by two close aides, Michael Deaver and Peter Hannaford, represented the Republic of China (Taiwan) at the same time they were helping write speeches on the subject for Reagan, who advocates having an official liaison mission in Taiwan.

"Hell, I was the one who was selling them on Taiwan," Reagan said.

Discussing economic issues, Reagan made his customary criticism of what he said were President Carter's attempts to reduce inflation by increasing unemployment. Reagan said his own goal would be "a job for everybody of working age that wants a job in this country."

Reagan repeatedly expressed confidence that he could carry out his promises to simultaneously reduce government spending, cut taxes and increase the military budget. But he said that if he were forced to choose between a balanced budget and one that was unbalanced because of necessary military expenditures, he would choose the latter.

Reagan was generally unspecific about how he would carry out a number of his proposals. He was critical of a variety of federal regulations, including affirmative action proposals that went so far as to encourage reverse discrimination. But he said he would not try to do away with affirmative action guidelines in federal employment although he might revise some of them to make them more "practical."

As an example of an impractical regulation. Reagan said that the federal government encourages the hiring of more blacks and women but doesn't allow employers to advertise saying that vacancies will be filled by minorities.

Reagan took a similar tack on legislation that sets environmental standards for clearn air and water. The laws are all right, said Reagan, but some of the regulations issued by federal departments should be relaxed so they are less onerous to business.

Reagan was at the midpoint of a week-lone eastern trip in which he met with executives and reporters of Time, Newsweek. The New York Times and Hearst Newspapers. He began the week with a Republican unity dinner in New York and will conclude it tomorrow afternoon with a unity reception and rally in Chicago.

These affairs are designed to pay off the campaign debts of the candidates Reagan defeated in the primaries. In return, they pledge their loyalty to Reagan in the fall election campaign.