President Carter's plan to restructure the nation's biggest welfare program passed a key House test yesterday.

By a vote of 209 to 177, the House killed Republican motion to open up the bill to a spate of amendments designed to gut major portions of the bill and reverse key provisions.

The legislation, requeste by Carter after an even more far-reaching measure failed last year on account of its cost, would establish for the first time a minimum level for state welfare payments under the program of Aid to Families with Dependent Children (AFDC).

Under this provision, once the program goes fully into effect in 1982, the states would be required to support needy families at a level of welfare benefits equal to 65 percent of the poverty line.

This works out to a benefit payment of $4,700 a year for a family of four without other income. At present, 13 states, all in the South or Southwest, pay less than this combined cash welfare and food stamp benefits. Mississippi only pays $1,440 in cash.The $4,700 guarantee would consist of cash and food stamps. About 800,000 families would receive improved benefits under this provision.

The use of the 65 percent-of-poverty formula provides an automatic cost-of-living escalator, since every time inflation raised the official poverty level, the minimum dollar payment requirement would automatically rise to meet the 65 percent ratio.

Bill provides about $730 million a year in federal fiscal relief to the states on their welfare programs. At present, the federal government reimburses each state from 50 to 78 percent of its AFDC outlays. The bill reduces each state's share by 10 percent, thereby providing the fiscal relief.

For this reason, the bill has strong support from the National Governors Association and many other state and local government groups.

The AFDC program supports about 7.5 million children and 3 million of their parents nationwide, at combined federal-state cost of about $12 billion. This means that one person out of every 20 in the country depends on it.

Rep. James H. Quillen (R-Tenn.), said the bill would provide for a "national universal guaranteed income." Rep. John Rousselot (R-Calif.), sponsor of a GOP substitute, said it needed stronger work rules for welfare recipients, a chance to let states force them to work off their welfare payments -- or "work-fare" -- and a stiffer assets tests to determine who should be eligible.

Rep. Trent Lott (R-Miss.), said, 'It'll cost taxpayers more, it'll put more people on the welfare rolls and it does not provide for workfare." They called on the House to defeat a rule for debate that would bar all major amendments.

However, Ways and Means Chairman Al Ullman (D-Ore.) said the bill doesn't provide and guaranteed minimum income except for those who cannot work. Persons able to be provided with normal jobs would be required to take them. "This is a sound, constructive" measure, he insisted.

A final vote on passage of the bill is expected next Wednesday. On yesterday's key vote, all Maryland Democrats except Beverly B. voted to kill the Republican move to open up the bill to amendments. Both Maryland Republicans voted for the GOP move. In the Virginia delegation, only northern Virginia Democrats Joseph L. Fisher and Herb Harris voted against the GOP move.