Courtney Riordan, head of research and development for the Environmental Protection Agency, has told a scientific symposium here that the credibility and independence of the agency's research arm is like that of a restaurant waiter who takes orders.

Riordan, an acting assistant administrator and one of two remaining high-level officials who served under former EPA administrator Anne M. Burford, said of the office of research and development, "We're not in charge. We're like a waiter in a restaurant."

"Our job is to do what the client wants . . . . We're saying that we're doing research because the client wants it, not because we need to know," Riordan said.

He did not identify his clients but, from the context of his speech, it appeared that he was referring to other EPA divisions. "We're always presenting a list of projects with no intellectual basis to fall back on," Riordan said.

Riordan's remarks at the annual meeting of the American Association for the Advancement of Science gave new evidence of disarray within the agency.

Newly confirmed EPA Administrator William D. Ruckelshaus is "aware of the problem with research," Riordan said, "not only with budgets but with its position in the agency.

"Over time, the research and development program must develop independence and credibility that will enable you to say no once in a while," he said.

According to an AAAS study, research at EPA was affected because "with the change in administration, there was a need to get the budget under control. Some research projects were considered inappropriate or better left to the private sector. R&D became a project of major reductions."

Since the Reagan administration took office, EPA research funds have been cut from $385.4 million in fiscal 1981 to $205.5 million in the administration's request for next year.

"We're under the gun on acid-rain research. We're under the gun to solve a problem to which there is no immediate solution. When money was made available in 1980 for acid rain, EPA scrambled to relabel research acid-rain research," Riordan said.

Criticizing political and regional pressures on the agency to study local problems, Riordan said he has been unfairly criticized for switching acid-rain research funding from the upper Midwest to New York state.

The decision was made for purely scientific reasons, but caused "a major political imbroglio," he said. "It was not a political decision based on apocryphal meetings I had with Anne Gorsuch Burford .

"The office of research and development ought to be independent in its advice to the administration," Riordan said.

"We need to do anticipatory research, to identify problems, to get the jump on problems," he said.

Other speakers at symposiums here this weekend suggested other factors that hurt the agency.

For instance, Marilyn C. Bracken, a former EPA associate administrator, discussed the magnitude of problems facing the agency.

"There are 60,000 commercial chemicals, excluding drugs and pesticides," she said.

"One thousand commercial chemicals enter the marketplace each year. There are really only 150 we have any health data on."