Immigration and agriculture may feed into a cycle that brings some farmers great prosperity while dragging seasonal workers into poverty, according to new research by two California professors.

J. Edward Taylor of the University of California, Davis, said Monday that studies he has completed with Philip Martin show the United States runs the risk of creating a new rural poverty if it does not change its immigration and integration policies.Taylor spoke during the annual meeting of the American Agricultural Economics Association, which runs through Wednesday in Salt Lake City.

A 1967 presidential commission found that the exodus of people from America's rural areas left those who stayed behind even worse off than they were before, Taylor said.

Now, 30 years later, the immigration cycle is contributing to another kind of rural poverty.

In a study of 65 rural communities in California's San Joaquin Valley between 1980 and 1990, Taylor and Martin found that the addition of 100 farm jobs resulted in an additional 139 people - including immigrants, their families and area residents - living in poverty.

Taylor said the cycle begins when new seasonal jobs are created in an area. Those jobs fuel increased immigration, often from Mexico in the case of the San Joaquin Valley.

But the easy availability of inexpensive workers encourages farmers to expand their labor-intensive operations and create new jobs, thus continuing the cycle, he said.

And Taylor said the problem is not limited to California. According to the professors' research, the creation of an additional farm job led to a reduction in the number of people living in poverty and using welfare nationwide during the 1970s. But during the 1980s, he said, each additional farm job had the opposite effect.

"We're finding that the immigration of low-skilled people into rural communities . . . leads to an increase in poverty," Taylor said.

He said some farmers are ignoring the social costs of increased poverty when they plant labor-intensive crops.

The federal government's efforts to solve the problem by tightening border controls could reduce the availability of workers, Taylor said. But he has not seen any indication that those policies are working.

In addition to those attempts, he said, farmers need to receive incentives to use methods that do not require as much labor. That could reduce the demand for immigrants and help stop the poverty cycle.