The Arizona Legislature gave preliminary approval Tuesday to a proposal that would allow the police to arrest illegal immigrants on trespassing charges simply for being in the state.

The provision, which opponents and proponents call a first in the nation, is part of a wide-ranging bill whose sponsors say they hope will make life tougher for illegal immigrants.

The House bill must be reconciled with a version passed by the Senate, something that may be done within the next week or two. Both include measures to outlaw the hiring of day laborers off the street; prohibit anyone from knowingly transporting an illegal immigrant, even a relative, anywhere in the state; and compel local police to check the status of people they reasonably suspect are in the country illegally.

Immigrant advocates call the bill some of the harshest legislation they have seen in a state where battles over immigration are particularly sharp edged.

Its sponsors said Gov. Jan Brewer, a Republican facing a primary competition from conservatives, has indicated her support, though her spokesman said she would not take a position until the final bill reaches her desk.

State Senator Russell Pearce, a Republican and the chief sponsor of the legislation, brushed aside concerns raised by civil libertarians that the law would open the door to racial profiling. The local office of the American Civil Liberties Union says the bill is unconstitutional.

Mr. Pearce said the bill gives the police another tool and compensates for lax enforcement of immigration law by the federal authorities. The police, he said, do not have to arrest every illegal immigrant on trespassing charges, but it gives them that discretion.

"American citizens have a constitutional right to expect their rights and laws to be enforced," he said in an interview.

Several police chiefs and sheriffs have criticized the bill, calling it burdensome and impractical and a tactic that will scare immigrants out of cooperating with investigations and reporting crime.