President Carter declared snow-bound Buffalo, N.Y., a "major disaster area" yesterday as cold arctic air raced down the East Coast threatening freezing temperatures as far south as northern Florida.

The disaster declaration - which translates into more unemployment aid, extra money for snow removal and road maintenance and low-interest loans for home and business owners - was unprecedented in the United States in that disasters have never before been declared because of snow.

The President's order also covers nine western New York counties that have been virtually paralyzed by record snow accumulation and cold temperatures.

"They've not been able to collect trash or garbage in more than two weeks, said Carter, who dispatched his son Chip and presidential assistant Midge Costanza to the area Friday to asses the storm's impact. "Many cars are completely covered with snow and they've already found nine people dead in them," the President said. "The economic consequences are very severe."

As requests from other hard-hit states continued to pour in, Carter also declared a state of emergency - which provides federal manpower and equipment assistance but is a less-severe designation than "major disaster" - in Michigan.

So far this winter, disasters - designations normally reserved for areas hit with earthquakes, hurricanes or flooding - have been declared in New York because of snow, Florida because of unemployment among migrant workers, and Virginia and maryland because of the frozen condition of the Chesapeake Bay. Emergencies have been declared in Michigan, Pennsylvania, Indiana and Ohio. Cost of assistance to all eight states has been estimated at $50 million by the White House.

As extreme cold moved through the East, threatening to drive temperatures as low as last month's record low for the past decade, White House energy chief James R. Schlesinger said new supplies of natural gas from Western states and Mexico, authorized to be pumped east under emergency legislation passed by Congress last week, were helping relieve shortages but could only be considered stopgaps.

In Ohio, where industrial and school closings have been widespread, the sate government yesterday began running newspaper ads in natural-gas-producing Texas, Oklahoma and Louisiana seeking immediate delivery of large quantities of natural gas. "We've had four calls already," said Chuck Morris, spokesman for Ohio's Energy Emergency Management Commission.

Meanwhile, the National Rural Electric Co-operative Association asked Agriculture Secretary Bob Bergland to revive a loan program to help rural families insulate their homes and finance other energy-saving measures. It provided $47.7 million in loans until it was ended 1969.

Bergland, in a broadcast interview, said he has ordered his department's economic forecasters to stop making crop predictions "based on the assumption that we will have normal weather," which , he said, rarely occurs. He said the department will issue forecasts tied to varying weather predictions.

In the West, which has suffered from lack of snow while the East has had an excess, the Hyak Ski Corp., which operates a major resort in western Washington, sought help from a federal bankruptcy court, and Colorado prepared to embark on a massive cloud-seeding operation.

Locally the National Park Service began turning off the exterior lights at the White House, Washington Monument and Lincoln and Jefferson memorials Friday night in an energy-saving move even more stringent than was ordered during the 1973 Arab oil embargo, when the lights were kept on until 9 p.m. Lights at the Capitol and the eternal flame at President Kennedy's gravesite will be kept on, however.

Looking beyond immediate problems, Ohio Gov. James A. Rhodes invited governors of five other states that border on the Ohio River to meet with him Friday to discuss preparations for spring flooding.