"Every substance known to man can be described as toxic under some circumstances," said R. Leonard Vance, but that's no reason to regulate them. "If I take a 100-pound sack of sugar and drop it on your head from 10 feet, it can be toxic to you."

As the government scientist who decides when the Occupational Safety and Health Administration should stop talking about a health standard and make it law, Vance, 40, a lawyer and former chemistry professor, admits that he has been "very cautious" about imposing new standards. He has been so cautious that some critics say the Reagan administration has spent too much time talking about standards and not enough time enforcing them.

It wasn't that long ago, however, that Vance, as the chief environmental lawyer for the state of Virginia, made a habit of criticizing OSHA for dragging its feet on health and safety issues.

Now the new director of OSHA's Office of Health Standards Programs said he has "gotten a feel for the incredibly complex nature of the bureaucracy and the convoluted processes by which decisions finally are reached, finally delivered to, and imposed upon the public . . . . " And he said, "I don't think it's a matter of bad faith of individuals that results in government delay -- it's endemic to the system."

Vance was hired in April to fill the post, which had been vacant for nine months. A career appointee, he still commutes to Richmond on weekends to be with his family.

It wasn't long before Vance ran into controversy.

Several sources said he outraged many of his 30 employes by referring to some disgruntled workers as "communists." Sources said some of the employes sent him a letter, asking that he stop.

"I'm not going to get into personnel matters," Vance said during a recent interview, "but I never called anybody a communist."

The AFL-CIO and public health officials soon began blistering Vance, calling him the scientific hatchetman of OSHA administrator Thorne G. Auchter.

Under Auchter's leadership, OSHA has delayed a number of health standards written during the Carter administration and has proposed significant changes in existing regulations that define carcinogens and specify the medical records that employers must keep.

Vance said his staff is reviewing the standards to make them more cost-effective and efficient. But critics like George Taylor, an AFL-CIO safety expert, contend that Vance's real job is to make the rules more palatable to business. "The name of this whole game is dollars," Taylor said. "If it costs business too much, the standard is delayed."

"I've heard all of the charges," said Vance, "and they simply aren't true." The agency is rewriting the Carter-era regulations, he said, because that's "one of the prerogatives an administration has when it comes into power."

A number of OSHA career scientists said the agency was doing a bit too much tinkering earlier this year. They claimed the agency pressured them to make their scientific findings conform with Auchter's political agenda.

"Maybe some things like that happen," said Vance. "What I'm telling you is if they happened, they happen whether the Republicans or Democrats are in . . . . It's just part of government."

OSHA's primary job remains protecting workers, Vance said. Now, he said, OSHA also cooperates with business and looks for the most economical way to implement standards. "We must make sure that they have a sound evidentiary basis and also be the most cost-effective."

"I'm used to working in an environment of cooperation," he said. "In state government, labor, industry and environmentalists basically pulled together in a room and talked and talked and talked and took five years if it were necessary to come up with a regulation that most folks agreed upon.

"But at OSHA virtually every standard that we have promulgated has been litigated."