The backlog of patent applications for inventions in the biotechnology field has grown to 8,213, and some applicants are waiting almost four years for final action by the Patent and Trademark Office, a study says.

The General Accounting office, in a report released this week, said the inventory of unexamined biotechnology patent applications increased by about 33 percent in 1989 and 1990 and that efforts to accelerate the process "have been less effective than anticipated."Waiting time for biotechnology patents, the study said, averaged about 26 months last year, compared with a 19-month average wait in other technology fields.

Rep. Ron Wyden, who ordered the study by the GAO, the investigative arm of Congress, called the finding "very, very disturbing."

"These sorts of delays not only put struggling, young biotech companies at risk, they may also hold up distribution of new, lifesaving drugs, seed for supercrops or engineered organisms to clean up pollution," the Oregon Democrat said.

To obtain a patent, applicants must file descriptions of the new technology. Patent examiners then determine if the proposal is new, useful and significantly different from earlier patents. This requires experts, who understand the science involved, to search previous patent files.

Among biotechnology patents issued in 1989, those for genetic engineering inventions took the longest - an average of 47.4 months. Patents for immunology inventions took an average of 44.1 months and biochemicals 37.7 months.

The GAO said the Patent Office increased its biotechnology patent examiners from 91 to 112 from October 1988 to July 1990. It said more examiners could not be hired because the Patent Office lacked experienced senior staff to train the new employees.

The report said the lack of experienced examiners in biotechnology has caused the first examination of patent applications to be delayed an average of 13.1 months, compared with an average of 7.1 for all technologies.

Patent Office officials once set a goal of reducing the processing time for biotechnology applications to 18 months by 1992, but the report said the officials now believe they will be unable to meet that goal.