The Congressional reaction to President-elect Barack Obama’s reported $850 billion economic stimulus proposal was breaking down along partisan lines Friday, with Democrats expressing a willingness to work with the incoming White House administration and Republicans voicing skepticism.

Senate Majority Leader Harry Reid’s (D-Nev.) office sent an e-mail to the Democratic Conference late Thursday, setting “as close to Jan. 20 as possible” as the target for Congressional approval of Obama’s economic stimulus plan. Any hiccups would likely occur in the Senate, where early indications show Democrats receptive and Republicans prepared to oppose it.

“To take $850 billion just because we have a new administration — to rubber-stamp it — would be a big mistake,” incoming Republican Policy Committee Chairman John Ensign (Nev.) said in an interview on Friday. Ensign led last week’s opposition to Congressional approval of a financial bailout for the Big Three domestic automobile manufacturers.

An e-mail from Reid’s chief of staff, Gary Myrick, to Senate Democratic offices described Obama’s proposal as one that could include funding for energy, infrastructure, education, health care and “protecting the most vulnerable.”

Jim Manley, Reid’s chief spokesman, suggested that there was likely to be strong Democratic support for Obama’s plan, at least in spirit. Manley stressed that specifics remain to be developed, and he was clear not to voice support for or opposition to any particular dollar figure, $850 billion or otherwise.

“There’s strong support for a vigorous, robust package that will provide the biggest bang for the buck. The number discussed may or may not be correct,” Manley said. “We’re still working on the specifics. But in the end, we’ll only be able to do what we can get through the Senate.”

With an expanded 258-177 majority, House Democrats will be positioned to approve a stimulus package to their liking after the 111th Congress gavels in on Jan. 6. The House parliamentary rules provide the minority party virtually no avenues to bring opposition to bear on legislation.

But Senate rules afford the minority plenty of routes to hold things up and shape the final outcome of a bill, potentially giving the incoming minority of 41 or 42 Republicans a significant say in the final form of Obama’s stimulus legislation.

Privately, Senate Democratic aides concede that GOP cooperation will be necessary to approve the type of stimulus package being discussed. A senior Republican Senate aide signaled that the GOP Conference intends to shape Obama’s package to to fit its parameters.

“Before anything is passed, we’ll need to ensure that the funding is actually stimulative, that it’s not merely a series of earmarks disguised as ‘stimulus’ and that we’re not spending money we don’t have without any protection for the taxpayers,” this aide said.

“We’ll also want to take a look at what is timely, targeted spending, and what is merely a wish list of spending goodies that didn’t make the cut on the appropriations bills.”

Obama is set to be sworn in on Jan. 20, and his transition team has been in talks with Congressional Democratic leaders on an economic stimulus package with the hope that it might be ready to sign as soon as his first day as president.