The platform also proposes a constitutional amendment to ban abortion and affirms marriage as "the union of one man and one woman."

TAMPA, Fla. — The Republican National Convention adopted a 2012 party platform that advocates changing how U.S. senior citizens receive health care by shifting Medicare from a defined-benefit entitlement to a defined-contribution plan.

The platform also proposes a constitutional amendment to ban abortion without stipulating any exceptions for ending pregnancies caused by rape or to save a woman’s life. It also affirms marriage as “the union of one man and one woman.”

The platform would turn administration of the Medicaid program for 54 million low-income Americans over to the states. The outlines of the Medicare overhaul, which wouldn’t affect the 47 million current beneficiaries or anyone older than 55, are in line with the proposal to revamp the program by the party’s likely vice-presidential nominee, Rep. Paul Ryan.

“This ambitious blueprint projects a sea change in the way government works,” said Virginia Gov. Bob McDonnell, the platform panel’s chairman. States would “take center stage in the long-overdue renewal of our American society” through “reforming Medicaid and welfare programs and managing environmental programs locally.”

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The 2012 platform was adopted on a voice vote Tuesday as the convention opened in Tampa.

Both parties routinely approve platforms at their conventions every four years, meant to encapsulate their principles and goals. Much of their details are customarily ignored when it comes to actually governing.

Even so, a poll by the nonpartisan Pew Research Center found more people interested in the GOP platform than in the upcoming acceptance speeches by presidential candidate Mitt Romney and Ryan. The survey found that 52 percent said they were interested in learning about the Republican platform, compared with 44 percent interested in Romney’s speech and 46 percent interested in Ryan’s.

Calling Medicare “the largest driver of future debt,” the platform proposes giving senior citizens financial support, adjusted by income, to purchase private insurance. Such private plans would compete with the traditional Medicare program. To achieve further savings, the current Medicare eligibility age of 65 should be “made more realistic” because of longer life expectancy, the platform says.

The platform also calls for turning many of the functions of the Transportation Security Administration over to private businesses to provide security at U.S. airports.

In a boost for big coal-production states like Wyoming, Illinois and West Virginia, the platform advocates development of “state-of-the-art” coal-fired power plants and the new coal gasification and “coal-to-liquid” fuels.

The party affirmed its commitment to building the Keystone XL pipeline, which TransCanada proposes carry tar-sands crude from Alberta to refineries along the Gulf of Mexico. The Obama administration is reviewing a revised proposal after the president rejected the original route, which raised concerns it would damage environmentally fragile regions of Nebraska.

Republicans “respect the states’ proven ability” to regulate hydraulic fracturing to tap oil and natural-gas resources, the platform said.

On abortion, the platform advocates legislation to bar women from terminating a pregnancy for the purpose of selecting a child’s gender.

The constitutional amendment to ban abortion is a reiteration of the Republican Party’s longstanding position. The issue was thrust to the forefront of the political debate after Todd Akin, a Missouri congressman running for the Senate, said he opposed making an exception for rape because “legitimate rape” rarely leads to pregnancy.

The platform calls for a permanent ban on all federal financing of abortions; such a prohibition is enacted as a policy restriction to spending measures. The platform also advocates the end of any government subsidies for private health plans that provide abortions, although the party wouldn’t do away with tax benefits for companies that sponsor such coverage.

In a bow to supporters of Texas Rep. Ron Paul’s presidential candidacy, the platform calls for a commission to study the feasibility of returning the dollar to the gold standard. A similar commission created by President Reagan “advised against such a move,” the platform noted.

Democrats lambasted the platform and immediately sought to tie it to Romney, who has differed from some of its details. For instance, he has said he would allow abortions in cases of rape, incest or when the mother’s life is threatened.

Los Angeles Mayor Antonio Villaraigosa, who is among several Democrats in Tampa trying to get their party’s views heard, called the platform’s stances on abortion and immigration “draconian” and “extreme” and blamed Romney. “What you have seen from him is that he does one thing, he says another,” Villaraigosa said. “He has taken one position after another, time and again you know, and you can’t have it both ways.”