ON Nov. 20, 2004, Sergio Manzo-Jurado was watching the Montana state high school football championship with co-workers when a local police officer reported their presence to the Border Patrol. Despite a dispatcher's assurance that "the group was not creating any problems and did not appear to be doing anything illegal," Manzo-Jurado and his five companions were detained and questioned by an off-duty Border Patrol agent who had also been watching the game.

Although the officers concluded that Hispanic men speaking Spanish in public create "reasonable suspicion" that they are in the U.S.United States illegally, the 9th Circuit U.S. Court of Appeals disagrees. The court rightly rejects generalizations that cast large segments of the law-abiding population" into suspicion in its June 20 decision. But last week, the U.S. House of Representatives approved an amendment by Rep. John Culberson, R-Houston, that would encourage such outrageous arrests.

Culberson aims to use federal law to pressure so-called "sanctuary cities," including Houston, New York, Los Angeles and 29 other cities and counties, to change their police policies so that local officers can ask those they encounter for proof of their immigration status. For those cities that refuse to so direct their police, the amendment would cut off millions of dollars in federal crime-fighting funds. This amendment, while politically convenient this election year, would have some very damaging consequences if enacted.

Encouraging local officers to enforce immigration laws would replace the valuable respect and cooperation forged between police departments and their constituencies with a mutual suspicion and fear.

Officers, like those in the Manzo-Jurado case, would be required to see entirely legal behaviors as possible cause for arrest. Citizens and legal residents as well as illegal aliens and their families would avoid contact with the police, depriving officers of the essential help that witnesses and victims offer to solve crimes and prosecute violent offenders. This cooperation is particularly critical in cities like Houston, which experienced a 23 percent increase in its murder rate last year and is coping with its influx of Hurricane Katrina evacuees.

Local police departments cannot be all things to all people. By asking local agencies to enforce federal immigration statutes, Congress would overburden the already strained police forces of major cities. Those departments that currently instruct their officers not to inquire about immigration status are properly managing their police, directing them to focus on high priority violence, property crime, and possible terrorism.

Culberson's amendment would deny funds to the cities doing the most to focus their anti-crime priorities.

Finally, local police officers are untrained in federal immigration policy and cannot be expected to handle its complexities with the skill and experience that the U.S. Immigration and Customs Enforcement agents bring to the problem. By tackling violations of federal immigration law, inexperienced officers increase their department's liability in civil court.

In Katy, for example, police officers assisted federal officials in a 1994 immigration raid that mistakenly arrested 80 citizens and legal residents.

As a result of its participation, the Katy Police Department faced costly lawsuits from these individuals that it eventually paid to settle.

The Senate should carefully examine the consequences of this amendment and resist the partisan urge to adopt it as a way of proving their toughness on illegal immigration during an election year.

If senators join their House colleagues in enacting this hastily conceived measure, millions of Americans may find themselves detained for once legal activities, like listening to Latino music on the radio, reading Spanish language books and newspapers, or even speaking Spanish at a football game.

Dietert, a student at Baylor University, is a research associate at the Criminal Justice Policy Foundation in Silver Spring, Md. The foundation is a nonprofit that promotes solutions to the problems facing the criminal justice system. He can be e-mailed at zach@cjpf.org.