The government has evidence that as many as a quarter of a million workers face increased risk of cancer, heart disease and lung disease because of exposure to work-place chemicals, but it has declined to inform the workers, two consumer activists charged yesterday.

Ralph Nader and Dr. Sidney Wolfe, director of the Public Citizen Health Research Group, said at a news conference that the Health and Human Services Department this year rejected the Centers for Disease Control's request for $4 million to notify workers of the potential hazards of their jobs.

Calling that decision "unethical and immoral," Nader and Wolfe called on President Reagan to order that the workers be alerted so that they might seek medical attention.

The health threats were identified in dozens of studies conducted over the past several years by the National Institute for Occupational Safety and Health, which is part of the CDC. Although the studies are used to help set work-place safety standards, current NIOSH policies do not require that individual workers be notified of the results.

HHS attorneys have determined that NIOSH's policy is legally defensible, but it has raised some painful ethical questions within the scientific agency, many of whose employes are medical doctors who take a pledge to protect human life.

For example, according to documents released by Nader and Wolfe, NIOSH found that 10,000 chemical workers exposed to ether were at higher risk of developing a lung cancer which has a "somewhat better prognosis for treatment" than others.

"The question is whether early diagnosis and treatment would be beneficial for the worker," NIOSH noted in a 1982 summary of epidemiological studies.

A 1983 draft report by the CDC Ethics Advisory Committee agreed that there is no legal obligation to notify workers. But the report also acknowledged that "NIOSH does have an ethical obligation to inform, particularly when NIOSH is the exclusive holder of data or when there is clear evidence of a cause-and-effect relationship between an exposure and a health risk."

Internal HHS documents suggest that the Reagan administration has strong reservations about the cost of such notifications, however. A February 1984 memo to Edward C. Brandt, assistant HHS secretary for health, said it could cost up to $300 for each worker notified.

Moreover, the memo pointed out that the only full-scale experiment in worker notification -- a 1980 pilot program that warned nearly 1,400 chemical workers in Augusta, Ga., that they were at increased risk of bladder cancer -- led to more than $300 million worth of lawsuits.

Nader and Wolfe said such lawsuits "will serve as a deterrent against future recklessness by industry," and they argued that the need to help workers protect themselves should take precedence over worries about legal action.

"The Reagan administration has demonstrated . . . that it is more concerned about an employer's potential liability than with ethical obligations to workers whose increased risk of disease is uncovered by NIOSH's studies," Nader said.

CDC officials acknowledged yesterday that HHS budget officials had turned down a request for money to notify some workers but said Nader's $4 million figure was too high. They declined to say how much the agency requested.