Veto-shy no longer, President Bush already is setting the stage for some dramatic showdowns with the opposition-controlled Congress this year by promising to reject at least a half-dozen of Democrats’ top priorities.

From stem-cell research and collective bargaining rights to spending on the war, Bush has made a series of early vows to block the Democrats’ leading proposals this year. The threats, while not unexpected, are a clear break from the president’s first six years in the White House, when he rarely threatened and only once actually carried out a formal veto.

Whether Bush will follow through on his promises remains unknown, but Democrats and Republicans agree that compromise between Congress and the White House will be increasingly difficult to achieve in the coming months.

“Despite the lip service paid to bipartisanship and increased cooperation, there are few tangible signs of that on Capitol Hill,” said a senior Senate Democratic aide. “The only question is, will President Bush work with the Democrats to improve his legacy in the final two years of his administration?”

But a GOP aide countered: “Obviously, the Democrats’ policies are not in line with the Republicans’. It makes perfect sense that a Republican president would issue veto threats.”

In his tenure, Bush has vetoed just one bill — a measure passed last year to expand federal funding for embryonic stem-cell research. The president made some other veto threats in the past, but not at the pace of the first two months of the 110th Congress.

So far, Bush once again has officially promised to veto a similar stem-cell research bill as well as a measure seeking to revise the nation’s Medicare prescription drug law, a bill to ease employee union organizing requirements, the 9/11 anti-terrorism measure over provisions providing new collective bargaining rights for airport screeners and a water quality measure that would expand certain federal prevailing wage requirements.

And just last week, Bush pledged to block the House Democrats’ supplemental spending bill for the war if it puts too many conditions and timelines on funding for the Iraq conflict.

“The showdown is coming,” predicted one Senate Republican leadership aide.

Sen. John Thune (R-S.D.) said many Republicans would welcome Bush’s more liberal use of the veto, saying the president should dig in his heels when it comes to flawed Democratic proposals. Thune said he believes Bush ultimately will be selective but will no longer shy away from rejecting unsavory legislation.

“There’s a really good opportunity for him, and really a lot of people want him to use the veto pen,” Thune said. “I don’t think he’s going to refrain from using it. He’s the backstop for the bad stuff.”

Indeed, Republicans know they must look to Bush as their safety net over the next two years. After nearly 12 years in the majority, they now face a two-seat party deficit in the Senate and a 16-seat disadvantage to the Democrats in the House.

In the previous three Congressional sessions, Bush often tried to circumvent a showdown with the Republican majority before a veto became necessary. Intraparty fights often occurred, but deals were nearly always worked out before legislation made it to the president’s desk for consideration.

Even with that in mind, Democrats still wonder whether Bush will make a stand with the veto.

“I would hate for his legacy to be that he vetoed a lot of stuff in his last two years,” said Sen. Mark Pryor (D-Ark.). “I’d rather he work with Congress to get a lot of constructive things done. Of course, that’s not been his style.”

Asked whether a threat of a Bush veto will dissuade Democrats from pushing pieces of their agenda, Sen. Tom Harkin (Iowa) said flatly: “Not one bit.”

Many Democrats believe the president is merely grasping for power in an increasingly difficult political environment. And, they contend, Bush can do little to boost his standing with the public, especially if he blocks passage of popular issues like stem-cell research or rejects Democrats’ timelines for an end to the Iraq War.

“I think he feels like he’s lost control of the government,” said Sen. Sherrod Brown (D-Ohio). “This is about trying to make himself relevant. He’s increasingly less relevant as a leader because our party isn’t listening to him.”

But Republicans argue that Bush is pushing back to protect his long-standing views, not merely posturing for political gain. Bush, they say, is simply standing firm on his Iraq policy, continuing his objections to expanding stem-cell research and countering Democratic bills Republicans view as unfairly catering to the majority’s labor union base.

“There are clear philosophical differences here,” said Sen. Johnny Isakson (R-Ga.). “And they are gravely underestimating the situation if they think he won’t use” the veto.

Freshman Sen. Benjamin Cardin (D-Md.) said that while it is the president’s prerogative to stake out his positions on legislation, he believes vetoes could backfire in this new Democratic-controlled Congress.

“One of the things it may do is help galvanize more support for overrides,” Cardin said. “Congress may assert its independence more for the executive branch.”

The jury is still out over whether Bush will have enough support to sustain any or all of his vetoes. Many lawmakers privately suggest he may again corral enough votes to maintain a block of the stem-cell bill and perhaps hold tight on his war funding priorities. Other Democratic priorities, however, may win out, they said.

Senate Republican Conference Chairman Jon Kyl (Ariz.) said Bush is responding appropriately for a president of the opposing party, adding that the vetoes promised so far this year are on “highly contentious issues” that reflect serious differences between the parties.

“This isn’t about power,” Kyl said. “This is about furthering our agenda. In case after case, he’s not using the veto as an offensive weapon.

“It’s a defensive weapon to make sure something bad doesn’t happen.”