The degradation of farmland, spreading pollution and rising sea levels threaten to force millions from their homelands, creating a massive "environmental refugee" crisis for the world, says a new report issued Saturday.

The report by the Worldwatch Institute, a research group, estimated there are 10 million "environmental refugees" worldwide, almost equalling the 13 million officially recognized refugees who have fled war zones or political, racial or religious persecution.It noted most authorities currently do not recognize environmental decline as a cause of refugee movements but said the predicted advent of global warming will soon make the problem impossible to ignore.

"The expected rise of sea level because of global warming threatens to reduce the planet's habitable area on a grand scale, perhaps forcing the evacuation of lowlying cities and agricultural land throughout the world," said the report, entitled "Environmental Refugees: A Yardstick for Habitability."

Even now, the report said, "Vast areas are becoming unfit for human habitation. The growing number of people fleeing from environmental decline adds a new dimension to an already controversial global refugee problem.

"The vision of tens of millions of persons permanently displaced from their homes is a frightening prospect, one without precedent and likely to rival most past and current wars in its impact on humanity," the report said.

The report said degradation of agricultural land through poor soil conservation and farming practices and overgrazing is the most common environmental reason people are forced to leave their homes.

The "desertification" of farm and rangelands is now most serious in Africa, but the report noted the same problem was central to John Steinbeck's novel "The Grapes of Wrath," which chronicled the migration of Midwest farmers to California in the "Dust Bowl" days of the 1930s.

"Though Steinbeck never used the term, his `Okies' were environmental refugees," the report said. "Unsustainable farming practices had impoverished soils and made them more vulnerable to erosion by wind and rain.

"As the drought that became a hallmark of that decade deepened, rural peoples' economic margin of safety vanished along with their topsoil. Today, this story is repeating itself in many parts of the world."

The report said land degradation has become so widespread that a recent United Nations study estimated that 1.8 billion acres of land around the world - roughly 35 percent of the Earth's lnd surface - are in various stages of desertification.

Altogether, the report said studies indicate 135 million people inhabit areas undergoing severe desertification.

While land degradation is now the main factor in creating environmental refugees, the report said r

sing seas causeb by global warming was the problem of the future.

Scientists say the accumulation of heat-trapping industrial gases in the atmosphere is expected to raise global temperatures by several degrees over the next century. They predict the warming trend will raise ocean levels by accelerating the melting of polar icecaps. In addition, water expands as it is heated.

If ocean levels rise by three feet - well within the range of current projections - land supporting some 50 million people will be flooded, the report said.

It noted a recent study by the Woods Hole Oceanographic Institute in Massachusetts estimated that, in Egypt and Bangladesh alone, some 46 million people in heavily populated, low-lying river delta regions would be threatened by rising seas.

The fate of some island nations, such as the Maldives in the Indian Ocean, may be worse.

"The small nation, made up of a series of 1,190 islands in atolls, is nowhere higher in elevation than 2 feet," the report noted. "If current (sea rise) projections are borne out, the Maldives may (be) washed from the Earth."

The report said other key factors in the creation of environmental refugees are:

-Industrial accidents such as the explosion of the Chernobyl reactor in the Soviet Union and the release of deadly gas in Bhopal, India. The report said more than 100,000 people were evacuated from their homes near Chernobyl.

-Long-term toxic contamination such as Love Canal in New York. The report said that, to date, 1,390 U.S. families in 42 states have been relocated under the federal Superfund toxic waste cleanup program because their homes were on land that was permanently contaminated.