Taking their long-running battle to the U.S. Supreme Court on Wednesday, Arizona and the federal government are set to square off over the state's bitterly disputed 2010 law designed to crack down on illegal immigration.

Among the law's most contested provisions are expanded powers for local police to demand proof of the immigration status of anyone they stop, and to arrest, without a warrant, those they suspect of being here illegally. Advocates for immigrants say such powers invite discriminatory racial profiling based on skin color and foreign accents.

The Justice Department, which immediately challenged the law and had parts enjoined pending a final ruling on its constitutionality, is not pressing the racial-profiling issue at the Supreme Court. Rather, it will argue that the federal government's authority in immigration matters, administered through the executive branch, precludes state lawmakers from acting independently.

The closely watched showdown in Arizona v. United States, with a ruling expected this summer, has immediate consequences in the five Southern and Western states with similar legislation, and in Pennsylvania, where 15 strict immigration-control bills are pending.

In briefs filed ahead of Wednesday's oral arguments, lawyers for Arizona said the state was the "gateway for nearly half of the nation's illegal border crossings" and had no choice but to respond with legislation to address the budgetary and public-safety problems caused by unrestricted illegal immigration.

Pennsylvania State Rep. Daryl Metcalfe (R., Butler), cosponsor of similar legislation in Pennsylvania, said in an interview that he empathized with Arizona.

"Absent federal action to protect Americans from the foreign nationals who invade our country," he said, "the only line of defense is at the state level. Either the Supreme Court will stand with the states - or handcuff them."

State Legislators for Legal Immigration, a 40-state group that Metcalfe founded, is among about 60 organizations that have joined in various "friend of the court" briefs to support or oppose Arizona. Among the supporters are the Liberty Legal Foundation, the Minuteman Civil Defense Corps, and Freedom Watch. Opponents include the American Civil Liberties Union, the Mexican American Legal Defense and Education Fund, and the American Bar Association.

"The Supreme Court's decision could have a huge impact in Pennsylvania," said Rudolph Garcia, immediate past chancellor of the Philadelphia Bar Association and an outspoken critic of Metcalfe's legislation. "One of the reasons such bills have not been successful here is the existence of constitutional issues that the Supreme Court is about to address."

The stated goal of Arizona's two-year-old Support Our Law Enforcement and Safe Neighborhoods Act, more commonly known by its shorthand name, Senate Bill 1070, is "attrition through enforcement," a strategy that ratchets up pressure on illegal immigrants to the point where they decide to leave for less-restrictive states, or return to their home countries. This is what Republican candidate for president Mitt Romney means when he talks about getting illegal immigrants to "self-deport."

Representing the United States, U.S. Solicitor General Donald Verrilli Jr. is expected to argue Wednesday that Arizona's law conflicts with the federal government's sole power to decide who can stay in the country.

Representing Arizona, attorney Paul Clement, of the Washington firm of Bancroft P.L.L.C., is expected to argue that Arizona's law is simply a practical means to cooperate with federal law enforcement, not to usurp it.

Various groups, for and against the Arizona law, plan to march and rally at the base of the high court's marble steps.

Justice Elena Kagan, who as an Obama-appointed former solicitor general defended federal immigration policy, has recused herself. That leaves eight justices to hear the case, and the possibility of a 4-4 tie, which would let stand the circuit court ruling that blocked most of S.B. 1070, but would not quell the increasingly angry national debate about illegal immigration.

With notable impact in this election year, Lyle Denniston, who has covered the high court for 54 years, wrote this month in the Supreme Court's authoritative SCOTUSblog, "The court will conclude its hearings for the term ... by examining what the Constitution says about who can regulate immigrants lives. Its final ruling is likely to emerge by early summer, when the election campaign will be in full swing."

Contact Michael Matza at 215-854-2541 or mmatza@phillynews.com.