Stephen Crowley/The New York Times

Representative Dennis J. Kucinich, Democrat of Ohio, said today that he plans to support the health care bill when it comes up for a vote this week. He becomes the first Democrat to publicly disclose his intention to switch from a no to a yes vote on the legislation.

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“I’ve decided to cast a vote in favor of the legislation,” Mr. Kucinich said at a morning news conference in the Capitol. “If my vote is to be counted, let it count now for passage of the bill, hopefully in the direction of comprehensive health care reform.”

Mr. Kucinich said he was “quite aware of the historic fight” underway and decided to drop his opposition that the bill did not go far enough. He said, “I believe health care is a civil right.”

In an interview five days ago, Mr. Kucinich said he could not support the legislation and dismissed suggestions that his vote would derail the Democratic health care agenda. But since then, the congressman has come under extraordinary pressure from groups across the Democratic spectrum, including Moveon.org, which encouraged him to support the bill.

He said he still did not think the legislation went far enough — he has long advocated a single-payer system — but said his objections should not stand in the way of the bill.

“In the past week it’s become clear that the vote on the final health bill will be very close,” Mr. Kucinich said. “I take this vote with the utmost seriousness. I’m quite aware of the historic fight, which has lasted the last century.”

He added: “The president’s visit to my district on Monday underscores the urgency of this vote.”

In a private conversation aboard Air Force One, en route to Ohio on Monday, President Obama pressed Mr. Kucinich for his support for the bill. The White House did not know what the congressman had decided until earlier today, when his aides advised administration officials and House Speaker Nancy Pelosi of his plans.

While supporting the Senate bill, Mr. Kucinich said he did not like the procedure that might be used to pass it without an up-or-down vote in the House.

“I don’t like much of anything about this process,’’ Mr. Kucinich said.

Explaining factors he had considered in making his decision, Mr. Kucinich said, “We have to be very careful that the potential of President Obama’s presidency not be destroyed by this debate.’’

Mr. Kucinich said he would vote for the Senate bill even though he believed it was seriously flawed.

“Something is better than nothing — that’s what I keep hearing from my constituents,’’ Mr. Kucinich said.

The congressman said he would keep working for a government-financed single-payer health care system.

“I don’t like this bill,’’ Mr. Kucinich said. “But I made a decision to support it in the hope that we can move toward a more comprehensive approach.’’

Mr. Kucinich said he had not received anything from Congressional leaders or the White House in return for his support.

“There was no Nebraska or Louisiana type deal,’’ Mr. Kucinich said, referring to states that received extra Medicaid money in the Senate bill.

Mr. Kucinich’s support of the health care legislation gives Ms. Pelosi a bit of breathing room as she searches for 216 votes needed to pass the bill, in a vote that may be taken at the end of the week. But it does not end the vote-counting efforts that are continuing on Capitol Hill, where Democrats are still trying to persuade other undecided lawmakers to support the measure.