A Ralph Nader-founded health group charged yesterday that the Occupational Safety and Health Administration has made "a shambles out of worker health and safety protection" since the Reagan administration took office.

But OSHA administrator Thorne G. Auchter called the new report "hogwash" and maintained that his own figures show "tremendous improvement of every aspect of the agency's function, without exception."

The Health Research Group report said that the decline in the enforcement effort at OSHA was echoed at the Food and Drug Administration and the Environmental Protection Agency.

A report issued last week by the Sierra Club and other environmental groups also chastized OSHA for its "failure to enforce strong, existing safeguards" and its weakening of health standards.

Yesterday's report provided a more detailed analysis of enforcement activity, comparing actions taken during the first eight months of 1982 with the same period in 1980, the last year of the Carter administration.

The group's charges and the responses by OSHA illustrate widely differing interpretations of what is happening at the agency:

* The number of workers covered by OSHA inspections fell by 41 percent and complaints by workers declined, indicating a "general loss of faith in OSHA" by workers, the study said. Auchter called the first number "off the wall" and said the drop in complaints indicated more rather than less satisfaction by employes.

* "Establishment" inspections dropped by 17 percent, the group said, including a 54 percent drop in inspections following complaints and an 86 percent drop in follow-up inspections. It complained that the type of inspections shifted, that they were shorter in duration and that fewer people were doing them.

The group acknowledged, however, that "general schedule" or targeted regular inspections increased by 29 percent and when a new type of inspection is included, in which a company's records are inspected to see whether worker injuries and illnesses are frequent enough to warrant further inspection, overall inspections dropped by only 3 percent.

Auchter argued that the inspections shift was a "deliberate attempt" to get "the biggest bang out of the inspection dollar" and that general-schedule inspections of targeted industries with the worst health and safety records, those in manufacturing and construction, had doubled. Efficiency has also improved, he said.

* There have been "major decreases in violations and penalties" for companies that fail to comply with the law, the group said, with a 50 percent drop in serious violations, an 86 percent reduction in willful violations and a 65 percent decrease in repeated violations.

Auchter responded that violations and penalties were down as the result of a "settlement policy," which he said was instituted at the end of the Carter administration. He said that it requires companies to fix the hazards but may mean fewer citations and court confrontations: "Our philosophy is one of safety and health and not of crime and punishment."

But the Nader group said that the changes it cited were the "truest measures of OSHA's declining commitment to worker protection."

Auchter, while conciliatory toward industry, was less so toward his consumer critics, saying that the report could best be used to "help me start my fire" this winter.