WASHINGTON -- Soon after Americans for Democratic Action endorsed Barack Obama last month, its leaders were e-mailing deep concerns over his flip-flops on the ADA's bedrock liberal beliefs.

With his party's presidential nomination secure and Democrats rallying behind him, the ultra-liberal freshman senator was making a mad dash to the political center in preparation for the general election. Positions on gun control, trade protectionism, terrorist surveillance, the death penalty and even his Iraq withdrawal plan were being abandoned, softened or blurred to make his candidacy less threatening to more moderate voters.

That has sent off alarm bells in the Democrats' liberal base in the past week or two, among both its foot soldiers in the blogosphere and its oldest leftist bulwarks of party orthodoxy.

Over at the venerable ADA, keeper of the liberal flame, e-mails were flying back-and-forth among its board of directors and other members who were troubled by Obama's sudden change of mind on issues near and dear to their heart.

"There's some concern that has been expressed in e-mails between the board and staff and some of our issue analysts," an ADA official told me. "There's a dialogue going on among people who are not sure what his remarks mean."

And no wonder. The freshman senator's apparent makeover for the general election abandons some of his party's most fervently held positions in favor of gun control, opposition to the North American Free Trade Agreement and opposition to the Foreign Intelligence Surveillance Act (FISA), which would give retroactive legal immunity to telecommunications companies that help the government intercept calls and e-mails from terrorists.

The concern bubbling up from the base ranges from feelings of betrayal to pragmatic, if grudging, acknowledgement that he can't win the presidency unless he reaches out to the center where elections are won or lost.

"In the last week, Barack Obama has handed progressives a string of stinging rebukes," decried Democratic blogger Jason Rosenbaum on the far-left Huffington Post Web site.

"Am I bummed ... that Obama and most of our Democratic leaders caved in on FISA? Absolutely, and there's nothing wrong with saying so," said blogger Mike Lux at the Open Left Web site. And he's not alone. Others in the left's netroot armies are "writing about not lifting a finger to help Obama now that he's screwed us on FISA," said Lux, who nonetheless continues to support the Illinois senator.

Many of Obama's rightward shifts represent breathtaking changes from what he has long stood for, raising troubling questions about his character and becoming a major GOP attack line in the campaign.

On trade, for example, he recently told Fortune magazine that he would never withdraw from NAFTA, calling some of his sharpest anti-trade rhetoric "overheated." "I've always been a proponent of free trade," he said.

But he was fiercely critical of trade deals in his primary fight with Hillary Clinton, especially before union audiences, and he threatened to abrogate the pact with Canada and Mexico if they did not agree to changes in its terms.

In the aftermath of the Supreme Court's ruling that struck down the District of Columbia's gun ban, he issued a confusing statement that said he has always believed in the constitutional "right of individuals to bear arms." But he supported gun control as a state senator in Illinois, and a staffer told the Chicago Tribune last year that "Obama believes the D.C. handgun law (banning private ownership) is constitutional."

On FISA, he said earlier this year, "There is no reason why telephone companies should be given blanket immunity to cover violations of the rights of the American people."

But as the administration-backed FISA bill was cleared for debate last week in the Senate, he shifted sharply to the right, saying, "It is not all that I would want. But given the legitimate threats we face, providing effective intelligence-collection tools with appropriate safeguards is too important to delay."

Throughout his campaign, he has railed against "tax breaks for big corporations" and attacked John McCain's call for cutting corporate tax rates. But in a recent interview with the Wall Street Journal, he said he would consider cutting their taxes as part of a tax-simplification plan.

Even on the core issue of Iraq withdrawal, he seemed to be wiggling away from a full pullout. "Three or four of his Iraq advisers are hinting of greater flexibility," said Democratic defense analyst Michael O'Hanlon at the Brookings Institution. "That indicates the potential for some change in his previous position or at least some flexibility."

In a recent conversation with Iraq's foreign minister, Hoshyar Zebari, Obama reassured him that "he will not take any drastic decisions or reckless actions" and would consult "very closely with the Iraqi government and the military commanders in the field" before any troop withdrawals, Zebari told the Wall Street Journal.

All of these and other changes in his campaign positions were "signs of increasing maturity and growth" in the young senator, former Democratic National Committee chairman Steve Grossman told me.

Or are they, as the McCain campaign charges, Obama's willingness "to say or do anything it takes" to win the presidency?