President Carter will ask Congress this year for new health care benefits for millions of people -- the aged, the poor, workers and others who lack adequate coverage and, finally and perhaps most expensively, anyone with a major illness that outruns ability to pay.

The president has decided to make " $10 billion to $15 billion" worth of new coverage for these groups the "first phase" of his long awaited "National Health Plan," Health, Education and Welfare Secretary Joseph A. Califano Jr. announced here today.

Some of the new benefits would be paid by the government, Califano said, and some by employers under federally mandated programs. But aides said he was not ready to say how much each new program might cost, or how much employes themselves might have to contribute.

If Congress passed the program this year, Califano said, the coverage could start in October 1982, as the first "sensible," "moderate" and not over-costly step toward Carter's ultimate goal -- "universal, comprehensive" and thorough health coverage for everyone.

He offered only a few brief sentences describing this ambitious new plan, and department officials said details and a bill will not be ready for 60 to 90 days. An administration source said the few brief sentences are "practically all we have now."

Still, the announcement meant an important argument has been resolved: whether to make a major or "catastrophic" illness plan alone Carter's "first phase" toward complete national health insurance, or whether to offer what one official called "a little bit for everyone."

Administration economic officials argued for perhaps $7 billion to $9 billion worth of catastrophic illness coverage alone, as one of the cheapest ways to expand Americans' health insurance. Califano, White House Domestic Council head Stuard E. Eizenstat and White House health officials argued successfully for the broader approach, informed sources said.

Other forces, too -- particularly Sen. Edward M. Kennedy (D-Mass.) and organized labor -- also argued strenuously in behind-the-scenes briefings that a catastrophic illness bill alone would help the middle class, mainly, and do almost nothing new for the poor and disadvantaged.

AFL-CIO President George Meany, United Auto Workers President Douglas Fraser and Kennedy promptly attacked the new administration plan as far too limited.

They said the administration's planned cost controls on hospital revenues and doctors' fees are not tough enough.

And they said Carter's refusal to send a complete national health insurance plan to Congress in one package -- with provisions to phase in the various parts -- may mean the country will never have a complete health insurance plan.

The Carter plan "for all practical purposes abandons the president's commitment" -- first made in 1976 and often repeated -- to give all Americans adequate health insurance, Meany charged.

He called the Carter plan "vague" and "meager." Fraser and Kennedy used similar language. The chances of getting Congress to enact Carter's "first phase," then "winning five or six or seven" new congressional battles in coming years are "minimal," Fraser argued.

Fraser, Meany and Kennedy promised to work for a comprehensive plan to be completed in mid-April by Kennedy, labor and the Committee for National Health Insurance, a coalition of consumer, elderly and other groups.

Califano, however, said "the over-whelming sentiment among legislators" and others who favor national health insurance is that Congress "cannot and will not digest" a complete plan "in one bite." The president's plan meets today's economic realities, he argued, and will include such strong cost controls that much of the added cost will actually be no addition at all because of the savings.

But a prerequisite, he added, must be congressional passage of the present Carter bill to control hospital spending if hospitals' own efforts fail. "Only when we contain" unnecessary health costs, he said, "can we responsibly seek to implement" new benefits.

Califano told reporters he hoped for an accommodation with Kennedy and labor, because if the nation is ever to have broader health insurance, "we need a much broader coalition than we have ever had before."

Next Tuesday, however, Califano must testify before the Senate Finance Committee, where Chairman Russell B. Long (D-La.) is backing a set of bills that includes one to cover Americans' catastrophic illnesses alone. Some Congress watchers think this bill could be the one with the best chance of passage this year.

Califano presented the Carter plan while dedicating a New York University health care center designed to cut 40 percent off the cost of caring for convalescing patients. He praised the NYU center for holding its annual average increase in spending to 6.6 percent in the past three years, proof, he said, that hospitals can control costs if they try.

The handsome new $25 million Arnold and Marie Schwartz Health Care Center was financed wholly by the Schwartzes. He is a retired oil distributor. She is the former Marie Smith, a former Washington Post reporter who covered White House women's and cultural affairs until marrying Schwartz.