Washington ? Whither the youth vote? A year after backing Barack Obama by an overwhelming 2-to-1 ratio, young adults are quickly cooling toward Democrats amid dissatisfaction over the lack of change in Washington and an escalating war in Afghanistan.

A study by the Pew Research Center, being released today, highlights the eroding support from 18- to 29-year-olds whose strong turnout in November 2008 was touted by some demographers as the start of a new Democratic movement.

The findings offer further proof that the coalition of voters Obama cobbled together in 2008 — including high numbers of first-timers, minorities and youths — are not Democratic Party voters who can necessarily be counted on.

While young adults remain decidedly more liberal, the survey found the Democratic advantage among 18- to 29-year-olds has narrowed — from a record 62 percent identifying as Democrat vs. 30 percent for the GOP in 2008, down to 54 percent vs. 40 percent last December. It was the largest percentage point jump in those who identified or leaned Republican among all the voting age groups.

Young adults’ voting enthusiasm also crumbled. In the presidential election, turnout among 18- to 29-year-olds was the highest in years, making up roughly 20 percent of the voters in many states including Virginia and New Jersey, partly from high participation from young blacks and Hispanics.

That percentage dropped by half for the gubernatorial races in those states last November where Republicans celebrated wins as black groups pushed Obama to do more to soften the economic blow from mortgage foreclosures and Latinos saw little progress on immigration reform. Young adults were also the least likely of any age group to identify themselves as regular voters.

“This is a generation of young adults who made a big splash politically in 2008,” said Paul Taylor, executive vice president of the Pew Research Center and co-author of the report. “But a year and a half later, they show signs of disillusionment with the president — and, perhaps, with politics itself.”

Democrats saw evidence of this last November, when Republicans toppled Democrats from power in governor’s races in New Jersey and Virginia. Young, minority and new voters who Obama pulled into the fold in 2008 didn’t turn out at the same levels for the two Democratic candidates. The same thing happened in the Massachusetts Senate race last month.

The lesson: Neither party has a hold on 18- to 29-year-olds. They tend to vote far less than other age groups, yet they have proven to be a powerful constituency if they are persuaded to vote.

Analysts say the findings reflect the fast pace at which young voters live their lives. “If you don’t respond to their needs, hopes or dreams quickly, they’re gone,” said Matthew Dowd, an independent political analyst who was a strategist in former President George W. Bush’s 2004 re-election campaign.

According to the Pew survey, large numbers of young adults said they personally liked the president but were dissatisfied with his rate of progress in changing Washington. Just 46 percent of 18-to 29-year-olds said they believed Obama had changed Washington, compared with 48 percent who said he had not.

Still, when asked why Obama hadn’t done more to bring change, young adults were somewhat forgiving, with about 60 percent blaming the president’s opponents and special interests; only 25 percent said Obama was at fault for not trying hard enough.