(Reuters) - Even before his running mate was booed by a lobbying group for older Americans on Friday, Republican presidential nominee Mitt Romney was losing support among such voters, whose backing is crucial to his hopes.

New polling by Reuters/Ipsos indicates that during the past two weeks -- since just after the Democratic National Convention -- support for Romney among Americans age 60 and older has crumbled, from a 20-point lead over Democratic President Barack Obama to an edge of less than 4 points.

Romney's double-digit advantages among older voters on the issues of health care and Medicare - the nation's health insurance program for those over 65 and the disabled - also have evaporated, and Obama has begun to build an advantage in both areas.

Voting preferences among seniors could change in the final six weeks of the campaign, but the polling suggests that a series of recent episodes favoring Obama and the Democrats could be chipping away at Romney's support among older Americans.

Romney's selection of Wisconsin Rep. Paul Ryan as his running mate put the federal budget and Medicare at center stage in the campaign. But the debate over spending and entitlement programs that Romney seemed to be seeking has not unfolded the way Republicans wanted.

At the Democratic convention in Charlotte, N.C., on Sept. 5, former President Bill Clinton gave a folksy but blistering critique of Ryan's plan to revamp Medicare, warning that it could leave seniors unprotected from escalating health care costs.

Meanwhile, Democrats' efforts to portray Romney as a wealthy former private equity executive with little sympathy for the less fortunate got a boost last week, from Romney himself.

On a secretly recorded video released by the liberal magazine Mother Jones, Romney was shown telling supporters at a $50,000-a-person fundraiser that 47 percent of Americans would never vote for him because they do not pay federal income taxes, feel they are "victims," and depend on government benefits.

Democrats accused Romney of dismissing a range of Americans, including elderly people who depend on government programs such as Medicare and Social Security.

Romney's campaign rejected that, but the recent polls suggest that such claims may be resonating with Americans aged 60 and older, who for months had been the only age group to consistently support Romney over Obama.

Analysts say that if Romney cannot reverse the trend among older voters, he is doomed on Nov. 6.

"If Romney loses seniors, he loses this election, period," said Jonathan Oberlander, a health policy specialist at the University of North Carolina. "A bad showing nationally (among older voters) does not bode well for Florida and other states with big senior populations."