In an escalation of protest tactics, five immigrants dressed in caps and gowns held a sit-in on Monday at the Tucson offices of Senator John McCain, calling on him to sponsor legislation to open a path to legal status for young illegal immigrants.

Four of the protesters, including three who are in the country illegally, were arrested Monday evening on misdemeanor trespassing charges. The three were expected to face deportation proceedings.

It was the first time students have directly risked deportation in an effort to prompt Congress to take up a bill that would benefit illegal immigrant youths.

Separately on Monday, a lawsuit was filed in federal court in Phoenix by a coalition of civil rights, labor and religious groups challenging the new Arizona law that allows the police to detain suspected illegal immigrants as unconstitutional, saying it would lead to racial profiling.

Though it was the fifth suit challenging the law, it was widely believed to have the best chance of being heard by the courts given the groups’ experience and the nature of the complaint.

Brooke Buchanan, a spokeswoman for Mr. McCain, said of the protesters, “The individuals have a right to peacefully protest in the senator’s office,â€