WASHINGTON - Adding heft to the tug-of-war over illegal immigration, a national group of state legislators led by Pennsylvania Rep. Daryl Metcalfe (R., Butler) has proposed eliminating "birthright citizenship."

Within minutes of the news conference Wednesday, a coalition of civil rights groups meeting across town threw its weight behind the preservation of automatic citizenship for anyone born on U.S. soil.

As interpreted by the federal government, the 14th Amendment, ratified in 1868, grants citizenship to the child regardless of the mother's nationality or immigration status.

"Hundreds of thousands of illegal aliens are crossing U.S. borders to give birth and exploit their child as an 'anchor baby' " to obtain residency and other benefits for themselves, Metcalfe said.

His group, State Legislators for Legal Immigration, was represented Wednesday by lawmakers from Oklahoma, Kansas, South Carolina, Georgia, and Arizona, though Metcalfe said that legislators from 40 states were members.

They presented what they called model legislation to correct the "misapplication" of the amendment. Metcalfe said his group would "push out" the model bill, and a companion legal document called a "compact," to the 40 states.

The lawmakers feel compelled to act, he said, because "Congress has been AWOL for decades" on immigration reform.

Oklahoma State Rep. Randy Terrill said the federal government had been "derelict in securing our borders." As a result, he said, states such as his, plagued by immigrant drug dealers, gangs, and prostitution rings, "are stepping up to the massive policy void left by the federal government."

Opponents predict the move will fail because immigration law is a federal prerogative. State laws that attempt to regulate immigration rarely pass constitutional muster.

By focusing on the interpretation of particular clauses in the 14th Amendment instead of seeking to repeal it, proponents of the legislation contend they are stepping into unexplored legal territory.

A subcommittee of Metcalfe's group began meeting in October to find ways to challenge "birthright citizenship."

"This is a soft step forward compared to what many thought we would do," Metcalfe said. "But we're not backing down."

A legal compact allows states to band together to propose solutions to federal problems, which then can be implemented subject to congressional approval.

The Metcalfe group's compact calls for participating states to "make a distinction in the birth certificates" between children born to mothers here legally - who fall under "the full jurisdiction" of the United States as defined by the amendment - and those whose mothers, the argument goes, do not fall under full jurisdiction because they entered illegally. In the latter cases, the lawmakers contend, the 14th Amendment should not apply.

The proposed legislation would also require every mother to prove her immigration or citizenship status before getting a birth certificate for her baby. States now have no such requirement.

Arizona State Rep. John Kavanagh said citizenship should not be based on "the GPS" coordinates of where a mother gave birth and the United States should not "give out citizenship like a door prize."

He said the proposed legislation would undoubtedly trigger legal opposition from pro-immigrant groups. "We're doing this the legal way," he said. "We want our day in court."

Immigration experts predict that the path of litigation would lead to the Supreme Court.

The hour-long news conference at the National Press Club was interrupted at least three times by opponents who had secretly seated themselves among reporters and suddenly jumped up. Several shouted questions and edgy comments. Two stood with a banner decrying the lawmakers' proposals as racism.

When the demonstrators refused to quiet down, they were forcibly removed by other observers who sympathized with the lawmakers.

The American Civil Liberties Union of Pennsylvania called on state lawmakers to reject the bill when Metcalfe introduces it in the current session. "The 14th Amendment provides protection from discrimination and ensures that citizenship is not prone to the political whims of the day," said Andy Hoover, ACLU of Pennsylvania legislative director.

Adopted after the Civil War, the 14th Amendment negated one of the Supreme Court's most infamous rulings, the Dred Scott v. Sanford decision of 1857, which held that neither freed slaves nor their descendants could ever become citizens because they were chattel.

The first sentence of the amendment confers citizenship on "all persons born or naturalized in the United States" - a simple but powerful idea, its supporters say.

"The 14th Amendment is about protecting fairness and equality in the United States, values that Pennsylvanians hold dear," Hoover said. "Metcalfe's bill is unconstitutional and would certainly be challenged and rejected if it somehow became law. Equality under the law does not depend on who your parents are or where they came from."

Metcalfe said he was ready for the fight.

"We like the 14th Amendment. We love the 14th Amendment," he said. "But it's time to apply it correctly."

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