Heath and Human Services Secretary Margaret M. Heckler told a National Urban League conference here yesterday that President Reagan's recent illness had created an opportunity to gain support for improved medical care, particularly for black Americans, who die younger and suffer more diseases than whites.

"Now is the time to say to an attentive nation that not only is the mind a terrible thing to waste, but so is the body," Heckler said. "Now is the time to say, 'It is simply not right that white Americans should be healthier than blacks.'

"Now is the time to say, 'It's not right that black infants should weigh less than white infants," she continued. "It's not right that black adults should be far more susceptible to serious disease than white adults. And it's not right that black seniors should expect to live fewer years than white seniors in the United States of America."

She said that her department's $317 billion budget was not large enough to resolve the health problems facing blacks. She said the National Urban League and other private groups needed to help, and congratulated the group for its interest in health care.

Heckler said a government task force recently identified six causes of disease and death "far more prevalent among black Americans than among whites," but she did not name them.

Also yesterday, AFL-CIO President Lane Kirkland said the labor and civil rights movements would outlive the "errors and aberrations of the last five years."