By David M. Herszenhorn

The White House on Friday said it would bar illegal immigrants from purchasing health coverage through a proposed insurance marketplace. But the administration also said that the federal government would continue to require hospitals to provide emergency treatment to illegal immigrants at taxpayer expense.

The question of how illegal immigrants would fare under a proposed overhaul of the health care system came into sharp focus on Wednesday during President Obama’s speech to Congress. Representative Joe Wilson, Republican of South Carolina, shouted “You lie!” when Mr. Obama insisted that his health care overhaul would not insure illegal immigrants.

And the Obama administration’s determination to show that immigrants will not benefit from the health system overhaul highlighted the extraordinary sensitivity to the issue at a time when lawmakers still remain divided over whether the government should pay to provide health coverage for all American citizens.

A White House spokesman, Reid Cherlin, said that the president’s proposals would bar illegal immigrants from purchasing private insurance through the new government marketplace, known as an exchange, and that verification of immigration status would be required for anyone seeking to purchase coverage.

Although Mr. Obama in his speech referred to his “plan,” the White House has not developed a written legislative health care proposal and does not intend to do so, instead relying on committees in Congress, which have drafted several versions of the bill, some running more than 1,000 pages.

Mr. Cherlin said the White House was considering various enforcement options, including the Systematic Alien Verification for Entitlements program, which states now use to prevent illegal immigrants from accessing government aid programs for which they are not eligible.

The White House said that illegal immigrants would still be able to purchase health insurance through the private market, as they can now, but acknowledged that the private market was certain to shrink after the creation of the new marketplace.

Many illegal immigrants must now seek medical treatment in emergency rooms, which by law cannot turn them away. In recent years, the federal government has spent $250 million a year to reimburse hospitals for bills that go unpaid as a result. The White House said those reimbursements would continue.

A draft of the health care legislation approved by the House Energy and Commerce Committee would allow illegal immigrants to purchase insurance through the new marketplace, but would bar them from obtaining government subsidies to help low-income individuals and families afford coverage.

Under that House bill, illegal immigrants would not be subject to a new requirement that all Americans purchase health insurance. Some non-citizens legally residing in the United States would be required to purchase health insurance, but they would be barred from obtaining subsidies even if their income were low enough to otherwise meet the eligibility requirements.

Senators who have been negotiating a compromise health care bill in the Senate Finance Committee said on Friday that they were contemplating steps to prevent illegal immigrants from benefiting from the health system overhaul, but some aides said they did not believe lawmakers intended to bar illegal immigrants from purchasing insurance at full cost, through the new exchange or otherwise, should they be able to do so.

The White House position could draw a backlash from advocates for immigrants.