President Carter is expected to choose in a matter of days between asking Congress for broad national health insurance for everyone in the nation and a far more limited, "targeted" plan to cover many fewer people and cost far less.

A last-ditch fight is going on at the highest administration levels over the president's choice. The decision could make a difference of tens of billions of dollars in the federal budget within a few years, sicne the broad plan is expected to cost the government $40 billion a year at the outset, while the more limited one would cost between $15 billion and $27 billion, according to Health, Education and Welfare Secretary Joseph A. Califano Jr.

The president has promised to send congressional health insurance backers his plan by late July.

In a confidential memo May 22 Califano told Carter that he "must make" a "fundamental" and "thresdhold" decision almost immediately on which "of these major forks in the NHI (national health insurance) road we should take."

A copy of the 17-page memo was obtained by The Washington Post. Comments on it by some of the administration's top budgetary officials - arguments for the limited approach - are expected to be ready for the president today, sources said.

One usually well-informed official said the president has already made his choice - to stick to his campaign promise to give Americans broad or "comprehensive" health insurance, even though it would have to be phased in over several years.

"No one expects a complete plan to go into effect tomorrow - Any comprehensive plan would start piecemeal," a congressional health aide said. "The argument is over whether the administration bill will specify the added steps to be taken year by year, or whether it will only call for limited measures."

Max Fine, director of the Committee for National Health Insurance - that cause's main lobby, heavily representing AFL-CIO unions - said, "We've been assured repeatedly, and as recently as this week, that the president will choose a broad, comprehensive plan."

But one high government official said, "I'm in no position to predict what the president will do."

Another highly placed administration official said, "I think most of us feel the president has already decided to go the broad way. But that may be wrong. He's changed his mind before. ANd the economi agencies - Treasury, OMB, the Council of Economic Advisers - are concerned about the impact of national health insurance on inflation, and they're pressing."

Top Office of Management and Budget, Treasury Department and CEA officials - most vigorously, OMB Director James McIntyre - want a plan that will cost the government as little as possible.

Specifically, some are urging federally guaranteed coverage only for the catastrophically ill, who can run up many thousands of dollars in health care bills, and for the poor.

Califano, White House health and domestic affairs officials and most other HEW officials have been urging the president to commit himself to the broadest possible program.

The Califano memo says the "broad appraoch that ensures [that] everyone in the nation will receive basic health benefits" could add $40 billion to the budget at the outset. It says the "targeted approach" - one that "guarantees basic health benefits to the very poor and only restricted benefits," such as catastrophic protection, to others - would add up to $27 billion.

OMB officials and others favoring the latter way have been writing the president their own memos, one source said, because they think Califano's memo does not present their views strongly enough.

But some supporters of broad insurance are saying the opposite - that Califano paints too black a picture of the possible economic repercussions of the broad approach and too rosy a picture of the advantages of a more limited one.

Califano said a broad plan "would sifnificantly affect efforts to hold the line" on the federal budget in the 1980's.

He saw a role for private insurers in any plan, though in any plan "extensive regulation of the private insurance industry would be necessary."

Only on May 20, two powerful senators - Russell B. Long (D-La.) and Abraham A. Ribicoff (D-Conn.) - submitted a catastrophic health insurance bill. The president said in Spokane may 5 that a federal plan might start with catastrophic coverage.

Most health authorities say they think such insurance would have huge appeal to middle-class Americans who already have insurance for most illnesses. But many economists say they fear such a plan would encourage still more spending on the last-ditch, highly technological care that is already costing billions yearly.

The president has promised to send Congress a plan so its main health insurance backer, Sen. Edward M. Kennedy (D-Mass.), can hold hearings on it before his health subcommittee starting in August.

But the most enthusiastic insurance advocates expect hearings and debates to stretch into 1979 and 1980. The current goal of White House advocates is to have the president sign a bill in 1980, the year of the next presidential election.