The Food and Drug Administration approved twice as many completely new drug compounds last year as it did in 1980, the agency announced yesterday. But the number of drugs in all categories that the FDA approved actually declined.

FDA said that 27 new chemical compounds were approved for use, the most since passage of the landmark 1962 legislation setting up the drug approval process, and an increase of 15 over the previous year.

New drug chemicals are only one category of drug approvals, but are considered, FDA Commissioner Arthur Hull Hayes Jr. said, to be a "very important indicator" because they are more likely to represent true innovations.

The FDA also approves drugs in new doses, combinations, marketed by new firms or for new purposes. When questioned yesterday, FDA officials said that, overall, the number of drug approvals dropped somewhat in 1981--from 114 the year before to 96.

In a press release, Health and Human Services Secretary Richard S. Schweiker said, "We promised the American people we would reform the drug approval process and last year marked a long step toward that goal."

Although the press release did not say so, Hayes and other agency officials noted in interviews that the increase stemmed in part from changes initiated by the Carter administration.

But Hayes maintained that the increase was also a response to a "new atmosphere" in the agency. "I do not believe efficiency and shortened time is inconsistent with the high standard of safety and effectiveness which the country expects, the law demands and which I am committed to uphold," added the FDA commissioner.

Hayes said that the average time to gain approval, particularly of "priority" drugs, had also fallen in recent years.

FDA statistics show that the period from submission to final approval of new chemicals has dropped from an average of 37.5 months in 1979 to 31.2 months in 1981. Similarly, for drugs considered to be important advances, the time frame has shrunk from over 17 months in 1976-78 to 10 months from then through '81. But, overall, approval time went from 33.6 months in 1979 to 21.3 months in 1980, then back up to 23.3 months in 1981.

A General Accounting Office report late last year concluded that since 1978 the FDA has "approved more drugs in less time than before despite an increased workload." But, GAO said, "it is too early to tell whether the positive trend will continue."

A spokesman for the Pharmaceutical Manufacturers Association yesterday praised the progress thus far. "This would appear to be a positive indication that FDA is making a serious effort to clear out the large inventory of applications which have accumulated over the years."

But Dr. Sidney Wolfe, head of the Public Citizen Health Research Group, cautioned that "if you look at the data on what drugs are approved in this country, most are not important therapeutic advances. They are advances mainly for the companies that thereby cash in on an already existing lucrative market."