With 5 million workplaces and only a few thousand inspectors, the Occupational Safety and Health Administration has to pick and choose where to make routine inspections.

In the past, industry has accused the agency of doing more nitpicking than choosing, but the Reagan administration is hoping to convert OSHA's harshest critics into self-policing enforcers of OHSHA standards.

Budget cuts have reduced the number of inspections the agnecy will be able to make by about 10,0000, down to 57,000, but the administration contends it can enforce its regulations better with less by more careful targeting of potential violators.

Reagan officials are looking at several plans to use OSHA resources better.

One idea is to look at an individual establishment's safety record and pass it by if it is clean.

Another is a program by which industry and labor unions would inspect their own workplaces and decide on ways of correcting any problems themselves.

One experimental project that has captured the particular interest and favor the Reagan officials was begun in March 1979 under the Carter administration. It is being conducted by a labor-management team at a Bechtel Corp. construction site of a nuclear generating plant in San Onofre, Calif.

The team consists of two members of management and two of labor, who all visit each part of the 21-acre site at least once a month and meet weekly to discuss safety problems. Local OSHA inspectors ocasionally inspect the inspectors.

Both Bechtel company officials and labor representatives say the program has worked well for all concerned.

This approach coincides with the administration's desire to end its adversarial relationship with business, and new OSHA head Thorne Auchter is particularly enthusiastic.

"That's a great program. We're really excited about it," he said.

Officials point out that as an experimental program it has much more oversight from the agency than could be maintained if all businesses were using this system, and they also say Bechtel was chosen in the first place for its safety record.

But Auchter also believes that one main reason why the pilot project has worked so well is that business and labor are doing it together for their mutual benefit.

"That's the ultimate solution," he says.