A prolonged and parching drought reduced stream flows to well below normal in 80 per cent of the nation last month, and groundwater levels reached record lows on a grand scale.

The Mississippi River, drainway of much of agricultural America, ran at about 60 per cent below normal, according to a new report by the United States Geological Survey. Together, the nation's "big five" rivers - the St. Lawrence, Columbia, Ohio, Missouri and Mississippi - averaged 40 per cent below normal.

The report also said ground water levels, which usually build in February to be tapped later in the year, declined in about half of the 140-plus observation wells used by the survey to monitor groundwater.

The survey findings come at a time of heightened concern over the effects of months of sparse rainfall on much of the nation's farmland. Dust storms, the shadowy specters of the 1930s that stripped fertile cropland bare, are increasingly frequent.

An Agriculture Department meteorologist said the next two to six weeks will tell what toll the dry weather will exact on the winter wheat crop, which helps to fill not only the U.S. bread-basket but those of many other nations.

The February measurements marked the third straight month of below-normal flows in the "big five" rivers. After above-normal flows in November, December was 6 per cent below normal, January 33 per cent and February 40 per cent.

Geological Survey scientists said some streams in the Pacific Northwest dropped to their lowest February levels in more than 70 years of recordkeeping.A hydrologist with the National Weather Service, Joseph A. Strahl, said yesterday that the Columbia River basin there is expected to get only half of its normal water supplies between now and October.

Strahl said the same crazy wind patterns that gave the country its bitter freeze also prevented normal winter rainfall.

Sixteen slow-monitoring stations in 10 states recorded their lowest flows for February since records were begun, in one case as far back as 85 years. The 10 states are California, Colorado, Hawaii, Idaho, Michigan, Wisconsin, New Hampshire, Oregon, Utah and Washington.

The drought has helped leave more than 17 million acres of land vulnerable to wind damage, according to the Agriculture Department, and another 3.8 million acres since Nov. 1 have already been reduced in fertility or productivity because of winds.

Topsoil from parts of Texas, Colorado and Kansas passed over the East Coast last week as a result of dust storms - the first time that has happened since the 1930s, an Agriculture spokesman said.

"Wheat is starting to green up" in some areas of the Great Plains, said Agriculture meteorologist Richard Felch, "but at the present time there is not enough moisture to carry for very long."

He said eastern Oklahoma has had some moisture but Kansas, eastern Colorado and most of Nebraska "remain pretty dry."

"There is a potentially very serious situation in store there," says Lester R. Brown, president of the non-profit Worldwatch Institute, a research organization here. He said that if harvests are substantially affected, near panic conditions could arise in other nations, "since the whole world is so dependent" on U.S. grain.