WHAT IS SAFE to breathe or eat, to work with or to wear?One can seldom be sure these days, because so many chemicals and minerals and additives and drugs are known (or thought) to be hazardous to health. Public confusion is compounded because government experts often seem unsure and make conflicting pronouncements about the same substance.

Thus there is good reason to applaud the plan for regulatory teamwork announced last week by four federal regulators - Environmental Protection Agency Administrator Douglas Costle, Occupational Safety and Health Administration chief Donald Kennedy, and Consumer Product Safety Commission Chairman S. John Byington. The four want to coordinate their agencies attacks on toxic substances and make their testing, rule-making and enforcement as consistent and cooperative as possible.

Apparently they want real collaboration to the point of sharing information, laboratories and expert staff. Ultimately, they envision uniorm policies for dealing with dangerous substances such as asbestos that are found in many places and pose many kinds of threats.

It's an ambitious plan. The obstacles are familiar and formidable: bureaucratic inertia and jealousies, congressional pressures, conflicting laws, the sheer complexity of the subject, the gradual fading of enthusiasm that undermines every innovation over-time. But the four agency head may just be determined enough to bea the odds and do the sensible reasonable and reassuring thing. Let us hope they are.