Health, Education and Welfare Secretary Joseph A. Califano Jr. says the federal government would be breaking a promise to Americans if it decided to withhold full social Security benefits until recipients reach age 68.

The stand pits Califano against Commerce Secretary Juanita Kreps, who says the government should consider deferring payment to full benefits as a means of restoring the foundering system to financial health.

"I absolutely don't agree with that." Califano said in an interview scheduled for radio broadcast Sept. 26.

"I think the the older Americans of this country have worked for years, 30, 40, some of them 50 years, and we have promised them that at age 65 there'll be Social Security benefits to help them have a comfortable and dignified life as senior citizens . . .

"If we want to defer the mandatory retirement age or eliminate it completely as a nation or states in this nation, that's fine, but! we should not break our promise to the American workers that they will be permitted to retire at 65 if they so choose to do under the current system."

By law, workers are entitled to partial Social Security benefits at age 62 and full benefits at 65. Many companies require employees to retire at 65.

Kreps has said officials are discussing the possiblity of withholding full benefits until retirees are 68. Actuaries predict the first of several Social Security reserve funds will go dry in fiscal 1979.

Kreps said it was "possible" the deferred-payment plan could become official policy "within eight years."

Later the White House put out a "clarification" statement saying the plan might be considered in the next century when Americans born during the post-World War II "baby boom" begin retiring.