The flood of Central American refugees trying to cross the U.S. border into Texas has slowed significantly thanks to help from Mexico, federal immigration authorities say.

Border security has been tightened in south Texas by the Immigration and Naturalization Service, INS officials say. In addition, the Mexican government has arrested 13,000 Central American refugees in the last six months, up from 12,000 during the previous year, INS says.James L. Buck, deputy immigration commissioner, told reporters Wednesday that Mexico has reinstituted checkpoints along that country's southern border and authorities are randomly stopping motorists to spot illegal aliens.

Buck said the number of border arrests of illegal aliens in south Texas has dropped from 200 to 300 a day to about 50 daily since a 400-member INS task force was assigned to Port Isabel, Texas.

The task force was set up to help stop the explosion of political asylum applications from Central Americans at the border. Between June and December of last year the INS was receiving an average of 5,000 asylum applications a month.

Most of the refugees were not eligible for political asylum because they couldn't satisfy the INS requirement that they demonstrate a well-based fear of persecution.

As many as 2,500 were detained at the Port Isabel facility, which now holds 1,500 aliens awaiting adjudication of their asylum claims. Another 1,700 have been deported, INS officials say.

The number of asylum applications submitted at the border has also dropped from 200 daily to only a handful, Buck said.

If current trends continue, "probably by the end of the summer, we will begin to see this entire task force sized down significantly," Buck said.

INS Commissioner Alan Nelson, meanwhile, credited the employer sanction provisions of the 1986 Immigration Reform and Control Act with helping to reduce the overall number of arrests along the 1,000-mile U.S.-Mexican border.