The more than $10 billion that American taxpayers give corn farmers every year in agricultural subsidies has helped destroy the livelihoods of millions of small Mexican farmers, according to a report to be released on Wednesday.

Prepared in advance of critical trade talks next month, the report by Oxfam International argues that the subsidies given American corn farmers allow them to sell their grain at prices far below what it costs to produce. That has led to cheap American corn flooding the Mexican market and pushing the poorest Mexican farmers out of business, the report said.

''There is a direct link between government agricultural policies in the U.S. and rural misery in Mexico,'' according to the report entitled, ''Dumping Without Borders: How U.S. agricultural policies are destroying the livelihoods of Mexican corn farmers.''

Like many other nongovernmental groups, Oxfam is working to promote changes in international rules at the meeting of the World Trade Organization in Cancún, Mexico, next month.