The Labor Department announced yesterday that it will stop enforcing 1,100 "nitpicking" job safety rules ranging from design specifications for toilet seats to the permissible size of knotholes in the siderails of stepladders.

Asserting that the safety of American workers is not threatened by the "shape of a toilet seat." Labor Secretary Ray Marshall told a press conference he is moving to junk such ruiles which have made the job safety program a laughingstock in the past.

"Thousands of working people suffer serious accidents and illnesses each year," said Marshall. "Yet to the best of our knowledge none of these accidents or illnesses has been caused by the shape of a toilet seat or because a fire extinguisher was two inches too low. That is why we are taking steps today to prune some of the underbrush that stands between OSHA (the Occupational Safety and Health Administration) and intelligently focused enforcement."

Most of the 1,100 doomed rules - roughly one-tenth of OSHA's entirt roster of health and safety regulations - were adopted without change from industry-devised guidelines when the agency was created in the early 1970s.

They quickly became potent weapons in the hands of OSHA critics seeking to ridicule the agency to death.

One of the critics' favorites was the requirement of "open-front type" seats on all toilets installed after June 1973. Another was a rule that fire extinguishers can be no more than 3 1/2 feet off the floor in some cases and 5 feet in others. Few critics failed to mention the 12-pages of fine print on the 1930s, the ice cut from ponds could not be used in watercoolers.

Marshall and OSHA Administrator Eula Bingham vowed to get rid of such rules when they took office last winter, but it has taken 10 people until now to accumulate the hit list, which will take 250 or more pages of a special adition of the Federal Register to explain.

The 1,100 rules cannot be dropped officially until after a review period of about five months, but Bingham said that in the meantime they will not be enforced by written notices or penalties.

A similar "de minimis" procedure - the government's way of saying that a silly, misdirected or outmoded rule will not be enforced to the letter - will also be followed in dealing with cases where technical violations of OSHA rules do not actually threaten the health or safety of workers, Bingham said.

"Employers will not be cited for minute differences in implementing the standard, as long as the intent of the standard is carried out," she explained.

Bingham and others said most of the 1,100 rules targeted for extinction were technologically obsolete or designed primarily to protect machinery. Some were simply aimed at improving comfort rather than promoting safety, the said.

Others were virtually indecipuerable. Some were written in Latin, said John Proctor, deputy director of OSHA safety standards, and "our people don't read Latin."

While some inspectors "winked" at the more ridiculous rules. Proctor said, regulations on the height of fire extinguishers turned up on OSHA's list of its 100 most violated rules.

Bingham said further streamlining efforts will be made in the future, including proposed revisions over the next few months in general industry standards covering walking and working surfaces, fire protection and machine guarding.