Sen. Russell B. Long (D-La) called on Congress yesterday to start insuring Americans against catastrophic medical bills by January 1981 "at the latest" instead of waiting for a broader Carter administration paln that could not take effect until late 1982.

The Senate Finance Committee chairman said the nation needs this "piecemeal" approach toward national health insurance, and he will lead a bipartisan fight to pass it this year.

Two important Republican committee members-Kansas' Bob Dole and Missouri's John Danforth-agreed, and said they and Sen. Pete Domenici (R-n.m.) have introduced a "Republican" Version of a catastrophic health insurance paln.

Long invited President Carter to join what will probably be a Finance Committee majority in this approach. And he said he was willing to "work with the president to see how much we can afford to go beyond catastrophic health insurance"-and even to spend $10 billion to $15 billion, the president's target figure for a start on national health insurance-in an attempt to get a start this year on broadened health coverage.

This apparent movement toward what could be the Senate's first new consensus on the subject in more than a decade came as the Finance Committee opened health insurance hearings.

What Long proposed was a measure to make sure most Americans are protected from any more that $2,000 worth of doctor bills or 60 days' worth of hospital bills in any one year.

Long has put his proposal in three bills so far. One is a plan he and Sen. Abraham Ribicoff (D-Conn.) have been sponsoring for nearly a decade-one that would also broaden Medicaid for the poor at a cost of around $20 billion.

Another Long bill would assessa 1 percent tax on employers for catastrophic coverage alone for employes and others.

And a bill he introduced Monday, dropping the tax idea and merely "mandating" employers to provide such coverage, adopts the approach President Carter is expected to take.

Health, Education and Welfare Secretary Joseph A. Califano Jr. last week said the president would ask Congress to enact a $10 billion to $15 billion "first phase" of a plan to include catastrophic insurance-but also help the aged, poor, disabled a(d "others" without adequate health coverage.

Long's payroll tax plan would cost only $5 billion to $7 billion by his staff's estimates. His newer plan might cost about the same.

But a a current national average of $215 a day for a hospital room, a sick person "might easily" run up $13,000 in hospital bills, as well as $2,000 in doctor bills, before any Long plan could help him, Califano testified yesterday.

"Millions of low-income families might be driven to financial despair" before qualifying, argued Califano - and covering "only" such high-cost care might encourage "profligate" spending by hospitals on the expensive methods that are jacking up health costs today.

Califano did not say how many dollars worth of catastrophic coverage the Carter administration is willing to buy or order, or how much its full "first phase" might cost the country beyond a $10 billion to $15 billion federal outlay. Some federal officials privately say they still do not have these answers, but the "thinking" is that the cost in public and private outlays would not go beyond $20 billion.

What Dole and his Republican colleagues are willing to buy is a plan to cost only $4 billion to $6 billion, with $3 billion of it in employer-employe contributions. Yet Dole said, the Republican and Democratic plans are "not entirely incompatible [and] I think we may have to votes" for an "affordable" bipartisan plan.