WASHINGTON, Jan 27 (Reuters) - The Obama administration told the U.S. Supreme Court on Friday that nearly all of President Barack Obama's healthcare overhaul can survive if the court declares unconstitutional the law's centerpiece provision requiring health coverage.

Administration attorneys argued in a written brief that all but two provisions can be separated from the requirement that Americans buy health insurance or pay a penalty by 2014, the law's cornerstone known as the individual mandate.

They said the 26 states and the independent business group challenging the law have failed to show that Congress would have wanted the entire law to fall in the event the individual mandate was struck down.

"Many provisions of the act, focused on controlling costs, improving public health and other objectives, have no connection to insurance coverage at all," Solicitor General Donald Verrilli wrote in the brief.

"And Congress directed that much of the act take effect several years before the minimum coverage provision's effective date, further demonstrating that Congress intended those provisions to operate independently," he added.

The Supreme Court has scheduled three days of oral arguments on the healthcare law for March 26-28, with an election-year ruling expected by the end of June.

The question of whether the rest of the law survives is one of four the court will consider, including the issue at the heart of the legal battle - whether Congress exceeded its powers in adopting the mandate.

The states and the business group have challenged the law as an unprecedented move that exceeds its constitutional powers and argued in written briefs filed last month the entire law must fall if the court strikes down the mandate.

Administration attorneys on Friday repeated their position that only two provisions could not be separated and would have to fall if the court invalidates the mandate.

Those provisions bar insurers from refusing to issue coverage to a person because of a pre-existing medical condition and from charging higher premiums based on a person's medical history.

But the government's attorneys said those challenging the law failed to show one instance when the Supreme Court in modern times has struck down a comprehensive law like the healthcare overhaul based on a finding that one provision exceeded Congress's authority.

Karen Harned of the National Federation of Independent Business said in response to the administration's filing that the group still believed the entire law must fall if the mandate is struck down.

"To argue otherwise would be like arguing a house can stand after its foundation has crumbled," she said.

The administration last month filed a separate brief with the high court defending the mandate as a constitutional attempt by Congress to address a crisis in the national health care market.

The Supreme Court cases are National Federation of Independent Business v. Sebelius, No. 11-393; U.S. Department of Health and Human Services v. Florida, No. 11-398; and Florida v. Department of Health and Human Services, No. 11-400.

For National Federation of Independent Business: Michael Carvin of Jones Day.

For Sebelius and the Department of Health and Human Services: Donald Verrilli Jr, Solicitor General of the United States.

For Florida: Paul Clement of Bancroft.

(Reporting by James Vicini)

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