President Bush has embarked on an ambitious campaign to win public support for his plan to reform the government retirement system known as Social Security. But some recent public opinion polls suggest support for the plan is slipping and even some Republicans in Congress are expressing doubts that the proposal will be passed this year.

The president has made Social Security reform his number one domestic priority. He is now in the middle of a 60-day nationwide campaign to convince the public that changes are necessary in order for the Social Security program to remain financially viable in the future.

"I am going to continue traveling over and over and over again making it clear to the American people that we have a problem," the  president said. "I am also going to travel over and over and over again to say to people who are receiving a [government pension] check and those near retirement, people born before 1950, that nothing changes."

The problem can be traced to an aging population of so-called Baby Boomers that will retire in huge numbers during the next several years. Five years ago, the number of Americans over the age of 64 totaled about 35 million. By the year 2050, that number will grow to 87 million.

At the heart of President Bush's Social Security reform plan is a proposal to allow younger workers to divert some of the taxes levied to fund the pension program into private investment savings accounts that they would control.

Democrats firmly oppose this part of the president's plan, arguing that it would deplete the Social Security program and force either tax increases or benefit cuts to keep it going.

Senator Ted Kennedy, a Massachusetts Democrat, urged the president to drop the idea of private accounts during a recent appearance on ABC's a This Week program.

"If the president is committed to destroying Social Security, which is privatization, then it does not make much sense to get into a negotiation," he said. "[If] he drops the privatization, you have an entirely different kind of circumstance."

Several recent public-opinion polls had good and bad news for the president's proposal. Most people surveyed agreed that Social Security needs reform. But increasing majorities in the polls also oppose the president's privatization plan.

"It is a very hard sell," said Stephen Hess, an expert on U.S. politics at the Brookings Institution in Washington. "It is a very important program. It has a very emotional content to it. It affects older people very viscerally and younger people worry about what their future will look like. He did not pick an easy one [issue]."

With Democrats united in opposition, the president must count on strong support from his Republican allies in Congress. But even some of them are warning the White House that the president may have to compromise with Democrats if he wants to pass an overhaul of the pension system this year.

"Enough congressional Republicans, particularly in the House [of Representatives] are concerned that even though they think this is a good idea, it could be the death knell for them politically because they will be up for re-election in 2006 [congressional midterm elections]," said Patrick Basham, who monitors politics at the Cato Institute in Washington. "The president has the luxury of not having to stand for re-election. And they [congressional Republicans] fear the power of the retired voter."

Political experts also say that the president is pushing hard for reform early in his second term because he knows his influence over Congress could diminish over time.

"And if it is to happen under this administration, under this president, it really will have to happen this year," said political analyst Stephen Hess. "Because this is the second term of a president who cannot run for re-election and in many ways the history of the American presidency is that the second term is something like an hourglass with the sands running out. He [Bush] knows that and he is campaigning on this almost as if it were a first-term, first-year issue."

The U.S. debate over pension reform is being closely watched by other countries where aging populations pose a daunting economic challenge.

By the year 2040, experts estimate that 26 percent of the U.S. population will be at least 60 years old, up from 16 percent just five years ago. By contrast, 28 percent of China's population will be at least 60 by the year 2040. The figures are even higher for Japan, Spain, and Italy where at least 45 percent of the populations will be aged 60 or higher 35 years from now.