Sen. Edward M. Kennedy and top labor leaders are getting ready to propose a new "Health Care for All Americans Act" that would drastically change the way the nation pays for its medical treatment.

In an interview, the Massachusetts Democrat conceded that the far-reaching bill he will introduced soon-which would privately insure almost everybody, but set an annual limit on the nation's total health spending-faces "an uphill battle."

Almost everyone else would call it an immpossible battle in this Congress. But Kennedy called an ambitious health insurance plan such as this "inevitable" at "some future date."

He also said that given the simultaneous appearance now of this bill, President Carter's less-ambitious plan and those of several other senators, this Congress may conduct "the first significant debate" in years on this issue, with "the strong possibility of some meaningful step."

His plan, he said, would cost the federal government an added $30 billion to $32 billion a year mainly to improve Medicare, and employers and individuals an additional $12 billion when fully in place.

But a first phase, he said, need cost no more than "the $5 [billion] or $7 [billion] or $9 billion" that has been cited as the cost of a catastrophic illness plan being pushed by Sen. Russell B. Long (D-La.).

The Kennedy Labor Plan was completed last week by a technical unit of the Committee for National Health Insurance, church and other groups.

The unit was headed by Dr. I.S. Falk, an emeritus Yale professor who heads the Yale-New Haven Community Health Plan. As a federal Official in the 1930s, Falk was known as "the architect" of Social Security.

Kennedy, the AFL-CIO, the United Auto Workers and the Committee for National Health Insurance plan a mid-April Washington press conference to unveil their plan.

But Kennedy confirmed the accuracy of a copy obtained by The Washington Post, and the fact that he and the labor leaders have abandoned their long-standing goal. That was a plan by which the government would have become virtually the country's only health insurer, paying doctors and hospitals what now would be $200 billion a year from federal taxes.

What Kennedy labor will propose instead is a plan to organize all commercial and nonprofit health insurers into four private consortiums to bargain with each state or area's doctos and hospitals on prices.

Individual insurers-such as Aetna, Prudential, Blue Cross-Blue Shield and other plans-would then sell coverage to employer-employe groups at premuims linked to wages and an employer's ability to pay.

Big, affluent employers would pay more-and thus subsidize the coverage of employes of less-affluent firms, as well as the self-employed, unemployed and others who today can buy only costly and inadequate health policies, if any.

Employers might have to pay at least 65 percent of their employes' health permiums in the plan's first phase. Employes could bargain for more coverage of benefits.

And insures like an Aetna, Prudential or Kaiser plan could make extra profit by better admistration fo deals with some dotors or hospitals to give care for lower rates. Efficient insurers also could offer subscribers cash rebates or added benfits.

"In this way we have strong cost-control incentives," said a Kennedy aide. "We have incentives for insurers, doctors and hospitals to keep their costs down so they can make a profit.

"We've taken the principles of social insurance, the principles of the Kennedy-labor plan-universal and comprehensive coverage, cost controls, quality controls-and applied them to private sector.

"Everybody would have a 'health card,' entitling him or her to care. But the doctor or hospital wouldn't know who was paying the bill."

The federal government would continue Medicare for the old and disabled. The federal-state Medicaid system would be largely wiped out, but states would continue coverage for dependent mothers and children and any poor who didn't fit in elsewhere.

The plan-like the plan President Carter has spoken about but not completed-would take full force in phases "over five to seven years," Kennedy said. But Congress would be asked to enact the whole plan in one bill. The president proposes only a first phase, with any later ones dependent on the country's ability to pay.

Kennedy maintained that his plan would do far more than the president's or any other to control costs, "because the first thing we would do would be the change in the system and the budget controls. A comprehensive plan like this is the only way we can get a handle on our exploding costs."