In his quest to pass health care reform, Senate Majority Leader Harry Reid (D-Nev.) is pursuing a potentially risky, step-by-step strategy that banks on momentum from the debate and a hard push from the White House to get the bill over the finish line this year.

As became apparent this week, Reid has secured promises from only most of his 60-member Democratic Conference to vote to begin debating the bill, but he has yet to nail down the votes needed to prevent a full-fledged filibuster of the package before passage. But aides and Senators this week said Reid is charting the only path he can on health care reform given the rules of the chamber and the Members with whom he is working.

“Sen. Reid is a creature of the Senate floor and isn’t a big fan of long-range planning because he knows you have to constantly adjust and change,— one senior Senate Democratic aide said. “So his approach is to get past one hurdle at a time and then set up for and worry about the next hurdle.—

So, for now, Reid has focused on just getting the bill to the floor, betting that once debate begins, Democrats will have a hard time voting against it.

“We need to get the bill to the floor,— another senior Senate Democratic aide said. “Then the real legislating will begin. Members will offer amendments and votes will be taken, and at some point we will have the votes to get a bill off the floor and into conference.—

A handful of Senate Democratic centrists have yet to agree to vote for a procedural motion that will allow the chamber to begin debate, but Reid has expressed confidence his Members will be on board once the bill has received a cost estimate from the Congressional Budget Office — something that may not be available for another week and a half to two weeks.

“Obviously he’s going to spend some time convincing people that we should move forward,— Democratic Conference Vice Chairman Charles Schumer (N.Y.) said Wednesday. “He’s making very good progress on that. … Not a single Democratic Senator has said they will not vote for the motion to proceed. The overwhelming majority have already said they will, and I believe by the time we’re ready to vote on it … that we’ll have the 60 votes.—

Of course, Reid has time to lobby centrists on blocking filibusters of both the motion to proceed and final passage. Democratic sources said Wednesday that the CBO cost estimate may not be ready until the week of Nov. 9. Reid had hoped to begin debate on the health care bill sometime next week, but he has promised his Members that a CBO score will be available before they have to vote.

Reid’s decision to move forward before securing the support of all 60 Democrats is part practical and part strategic, according to Democratic sources familiar with his thinking.

From a practical standpoint, it would be nearly impossible to corral all Democrats before the floor amendment process has even begun, considering many Members are inclined to withhold their support to try to influence the final bill.

“I don’t want to second-guess the leader’s decision. I think he needed to move forward, give us an outline,— said Sen. Sheldon Whitehouse (D-R.I.), a supporter of Reid’s approach. “For all of the Senators to sign up right now and say, ‘I’m on board with this bill’ — however it comes out — that is not leverage-maximizing behavior. So, I don’t think anybody’s astonished that people are still staking out positions and still expressing concerns.—

Strategically, the Majority Leader is wagering that — once the bill is on the floor — no Democrat will want to be tagged as blocking the party’s and President Barack Obama’s No. 1 domestic priority.

“I think the Senator knows that he has more room to work if this bill is on the floor,— a third Democratic Senate aide said. “The further down the road things get, the better the bill’s prospects are.—

But many have questioned why Reid chose to move forward with a bill that includes a controversial public insurance option, albeit with a provision allowing states to opt out, when including a “trigger— for the public option would likely have garnered at least one GOP vote. Moderate Sen. Olympia Snowe (R-Maine) has indicated she might vote for a bill if the public option was created as a fallback that would kick in only if private insurers could not reduce costs on their own.

Democratic sources said Reid realized last week that he did not yet have a solid 60 votes for either proposal but that he had more Democrats who felt comfortable with the opt-out option than he did for a trigger. So he decided to go with the majority of his party.

Democratic Senators supportive of the public insurance option on Wednesday defended Reid’s decision to include the measure in the final bill.

Schumer, who argued vigorously in favor of the public option with an opt-out, gave a vote of confidence to Reid’s strategy of incrementalism, saying he has been encouraged by the fact that centrists do not appear likely to block the bill from coming to the floor.

Schumer also said too much was made of Sen. Joe Lieberman’s (ID-Conn.) comments on Tuesday that he might vote to filibuster the bill if, in its final form, it includes a public insurance option.

“I thought the fuss made about what Sen. Lieberman said was greater than I anticipated,— Schumer said. “The fact that he said that he was definitely voting to move to proceed — on a motion to proceed — we regarded as a good sign, because he was one of the four or five people who in our view, hadn’t privately committed to that.—

Schumer also hinted at a strategy that Democratic aides said would likely be brought to bear on wavering centrists such as Lieberman, who caucuses with Democrats.

“We all know that the bill that emerges after weeks of debate on the Senate floor is not going to be the same one that leader Reid submitted,— Schumer added. “And I talked to Joe Lieberman later in the day and said, ‘Just keep your options open.’—

Indeed, aides said Reid would likely make the argument to moderates, after the bill has been through weeks of amendments, that the measure had been substantially changed and merits their support.

“Everything requires consensus that requires patience and negotiation,— the second Senate Democratic aide said. Reid “knows where he’s going and he’s determined to get there.—