The House last night approved a version of President Carter's plan to restructure the nation's largest welfare program, which now supports about one in every 20 Americans. The vote was 222 to 184.

The bill now goes to the Senate, where it faces imposing oppostion in the person of Finance Committee Chairman Russell B. Long (D-La).

The bill, proposed by Carter after an even broader plan failed last year on account of its cost, for the first time would set a minimum level for state welfare payments under the program of aid to families with dependent children.

Under the bill, once the program went fully into effect in 1982, states would be required to support eligible families at a level of benefits equal to 65 percent of the poverty line.

For a family of four without other income, this would work out at present to $4,700 a year. It would be payable partly in cash and partly in food stamps. About 800,000 families in 13 states of the South and Southwest that now pay less than $4,700 would benefit from this provision. As the cost of living goes up, the federal poverty level would automatically rise as well, because welfare benefits would be partially "indexed" to increases in the cost of living.

Reps. Barber Conable (R-N.Y.), John Rousselot (R-Calif.) and Robert S. Walker (R-Pa.) assailed the bill as a possible first step in creating a national guaranteed income.

"The national level of 65 percent is just a beginning," said Conable. He also said the bill does virtually nothing "to offer the states any real incentives or rewards to administer this program more tightly or target benefits on those of the greatest need" in order to reduce malingering and save money."

Rousselot charged that the bill "increases the welfare rolls substantially" by requiring all states (instead of the 26 who now do it voluntarily) to make eligible for welfare not just families where the father is absent or ill, but also families where the father is present but unemployed. At present 128,000 families are on the rolls in the 26 states which allow this. Enlarging the program to all states is estimated to make another 100,000 families eligible.

However, the bill's sponsor, James C. Corman (D-Calif.), said the bill -- whose annual cost above existing federal outlays would be $2.8 billion a year, of which $732 million would be in the form of fiscal relief to the states -- would help people at "the bottom of the ladder."

Who will benefit? he asked: "The aged, the blind, the crippled, the little children." The cost, he said, "is about the same as the nation's liquor bill. cAbout the same as the profits of oil companies go up when the prices of a gallon of gasoline goes up 20 cents."

Fortney (Pete) Stark (D-Calif.) said opposition to the bill came from "those who would starve children." He said the idea that 65 percent of poverty, or $4,700 a year for a family of four, is some kind of luxury income is absurd.

Republicans, arguing that the bill gives little work incentive and an unlimited blank check for states to draw on the Treasury to increase benefits, offered a motion to allow experiments by the states to greatly expand work requirements for welfare applicants, including making mothers of children under six work if daycare is available, and to give some states block grants in which a state is given a fixed amount and allowed to construct a program as it sees fit.

But Democrats let by Corman and Ways and Means Chairman Al Ullman (D-Ore.), beat it back before the final vote, 205 to 200. Conable ended up voting for the final bill after the GOP motion failed.

The fiscal relief in the bill comes in federal matching ratios. At present, the United States picks up 50 to 78 percent of a state's costs. The bill would reduce the state share by 10 percent.

The bill is part of a two-bill package of welfare proposals by Carter. The second portion creates about 600,000 new public service jobs, at a salary averaging $7,200 a year, as last-resort jobs for welfare clients, as alternatives to receipt of cash welfare payments. The jobs portion, estimated to cost $2.7 billion a year, hasn't received action so far in either chamber.