CHARLESTON, S.C., Oct 31 (Reuters) - U.S. President Barack Obama's administration asked a court on Monday to block parts of South Carolina's new immigration law, arguing the federal government had pre-eminent authority over immigration matters.

The U.S. Department of Justice sought an injunction in South Carolina against enforcement of portions of the state law, which toughens measures against undocumented immigrants and is set to take effect on Jan. 1.

The Department of Justice also sought a declaration from the court that provisions of the legislation were invalid on the grounds that they violated the Supremacy Clause of the U.S. Constitution and preempted federal law. "The United States Constitution forbids South Carolina from supplanting the federal government's immigration regime with its own State-specific immigration policy," said the filing submitted by U.S. Assistant Attorney General Tony West.

Obama's administration has already moved to challenge strict new immigration legislation in Alabama. Last month the U.S. Court of Appeals for the 11th Circuit granted the administration's request for a temporary injunction on two provisions of the legislation, including one that would permit the state to require public schools to determine the legal residency of children upon enrollment. However the court refused to issue injunctions on other provisions. Judges have also blocked parts of similar laws enacted in Georgia, Arizona, Utah and Indiana aimed at trying to deter illegal immigrants from coming to those states.

The South Carolina law, passed this year by a Republican-led state legislature, requires police to check the immigration status of people they suspect of being in the country illegally after stopping them for another offense.

A spokesman for South Carolina's Republican governor, Nikki Haley, who had signed the tougher immigration measures into law in the summer, said the state would fight to enforce them.

"If the feds were doing their job, we wouldn't have had to address illegal immigration reform at the state level," spokesman Rob Godfrey said.

Some conservatives complain the federal government has failed to sufficiently stop the flow of illegal immigrants into the country, forcing states to take action. Opponents of South Carolina's law say it would invite racial profiling.

There are an estimated 11.2 million illegal immigrants in the country, including 30,000 to 75,000 in South Carolina, according to the Pew Hispanic Center.

The law makes it a crime to knowingly transport or harbor an illegal immigrant and sets up a unit within the state police to deal with immigration issues and serve as a liaison between local authorities and federal officials.

Under the new law, employers will also be required to use the federal E-Verify system to check the citizenship status of employees and job applicants, and will face penalties for knowingly employing illegal immigrants.

In its filing to the Charleston Division of the U.S. District Court for the District of South Carolina, the Department of Justice said that, under the U.S. Constitution, "the federal government has pre-eminent authority to regulate immigration matters and to conduct foreign relations."

SOME PROVISIONS UNIQUE TO THE STATE

"Although states may exercise their police power in a manner that has an incidental or indirect effect on aliens, a state may not establish its own immigration policy or enforce state laws in a manner that interferes with federal immigration laws," said the filing submitted by West.

Opponents of the South Carolina immigration law welcomed the government action.

"We think they have done the right thing ... We urge them to file suit against the other unconstitutional anti-immigrant pieces of legislation that have passed in Indiana, Utah and Georgia," said Karen Tumlin, managing attorney for the National Immigration Law Center.

"South Carolina has a couple of provisions that are uniquely South Carolina," she said, citing a clause that criminalizes presenting false identity and the creation of a special immigration enforcement unit within the state police.

The Department of Justice filing said South Carolina's law, if allowed to go into effect, would undermine and disrupt federal agencies' existing immigration operations, "diverting resources and attention from the dangerous aliens whom the federal government targets as its top enforcement priority."

"It will cause the detention and harassment of authorized visitors, immigrants and citizens who do not have or carry identification documents specified by the statute," it added.

South Carolina Republican Representative Chip Limehouse of Charleston criticized the government's legal move as a "slap in the face ... to South Carolina."

Earlier this month, a coalition of civil rights groups filed a federal lawsuit to try to halt enforcement of the South Carolina law, calling it unconstitutional.

The government said the legislation targeting illegal immigrants passed by South Carolina and other states could result in damage to the United States' foreign relations and impede fair implementation of federal immigration laws.

The case is USA v. State of South Carolina and Nikki Haley in her official capacity as Governor of South Carolina, U.S. District Court, District of South Carolina.

For the USA: Tony West, Assistant Attorney General.

For the State of South Carolina: Not immediately available.

(Reporting by Pascal Fletcher)

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