By Eric Beech and Richard Cowan

WASHINGTON (Reuters) - Republicans in the U.S. House of Representatives unveiled an alternative plan to overhaul the nation's healthcare system on Wednesday, slamming Obamacare even as they aimed to keep some of its more popular provisions.

Their proposal, part of broader effort by House Speaker Paul Ryan to offer a Republican agenda ahead of the Nov. 8 elections, is conservatives' latest bid to "repeal and replace" the 2010 law.

Ryan, the country's highest-ranking elected Republican, is offering the proposal as the party seeks to maintain control of both the House and the Senate and take over the White House. Other proposals cover tax reform, address poverty as well as national security.

Republicans have challenged President Barack Obama's signature Affordable Care Act since it was enacted and have voted repeatedly to repeal it. Obama, a Democrat, has said it has helped some 20 million Americans get health care coverage.

Ryan acknowledged his agenda was unlikely to displace current law anytime soon.

"We're not going to repeal Obamacare when the current president of the United States is a guy named Obama," he told reporters. “What we are laying out today is a first-time-in-six-years consensus by the Republicans in the House on what we replace Obamacare with.”

In their plan, which is not formal legislation, House Republicans blasted Obamacare for limiting patients' choices, increasing consumer costs, and burying employers and health care providers under new regulations.

Ryan's proposal would keep some popular pieces, including not allowing people with pre-existing conditions to be denied coverage and permitting children to stay on their parents' coverage until age 26.

It would also allow states that have already expanded the number of people eligible for Medicaid under the law to maintain the additional coverage, although it would prevent any new states from doing so.

For people without insurance through their jobs, the Republicans would establish a refundable tax credit. Obamacare also provides subsidies for people to buy insurance if they do not qualify for Medicaid.

It also includes long-held Republican proposals such as allowing consumers to buy health insurance across state lines, expanding health savings accounts, reforming medical liability rules and giving block grants to states to run Medicaid programs for the poor.

Democrats, who have said they are open to tweaking Obamacare, dismissed Ryan's proposals as little more than warmed-over ideas that have long been in the Republican playbook.

House Republican would gradually raise the Medicare eligibility age, now 65, to match that of the Social Security pension plan, which is 67 for people born in 1960 or later.

Like Obamacare's so-called Cadillac tax on expensive healthcare plans offered by employers, which goes into effect in 2018, the Republican proposal would cap the tax deductibility of employer-based plans.

Industry groups struck a bipartisan tone in their reaction ahead of the election, as it remains to be seen who ultimately wins control of Congress and the White House.

"We stand ready to work with both parties on market-based solutions that improve access and affordability for consumers," said Marilyn Tavenner, president of America’s Health Insurance Plans.

(Reporting by Eric Beech, Caroline Humer and Richard Cowan; Writing by Susan Heavey; Editing by Peter Cooney and Jeffrey Benkoe)