WASHINGTON (CNN) -- Most of the 17 Democratic senators who are uncommitted superdelegates will endorse Sen. Barack Obama for president this week, sources told CNN Monday.

Sen. Barack Obama is expected to pick up superdelegate endorsements after Tuesday's contests, sources say.

The lawmakers will wait until after the South Dakota and Montana primaries Tuesday before announcing their support for Obama, two sources familiar with discussions between Obama supporters and these senators told CNN's Gloria Borger.

Obama supporters have been "pressing" for these superdelegates to endorse early this week, but according to one source, "the senators don't want to pound Hillary Clinton, and there is a sense she should be given a grace period."

A series of meetings on the topic have been facilitated at different times by Illinois Sen. Dick Durbin, former Senate Minority Leader Tom Daschle and Iowa Sen. Tom Harkin. Durbin and Daschle are Obama supporters, while Harkin is uncommitted.

Obama is now 46 delegates short of the 2,118 needed to clinch the Democratic nomination, while Clinton needs 202. There are 31 pledged delegates up for grabs in the Tuesday contests, and 202 superdelegates have yet to commit to either candidate. Watch how the race could end »

Obama has the support of 331 superdelegates to Clinton's 292.

Superdelegates are party elected officials and activists who are free to vote for either candidate.

Best Political Team Join the best political team as voters in the final two states cast their ballots.

Tuesday, 8 p.m. ET see full schedule »

Following Sunday's Puerto Rico primary, Obama picked up two more superdelegate nods, and Clinton received one.

Senate Majority Leader Harry Reid and Speaker of the House Nancy Pelosi will remain uncommitted until Clinton officially drops out of the race, sources told CNN's Candy Crowley, but that isn't stopping the two party heavyweights from using their clout to bring the primary battle to a hasty end.

Pelosi told the San Francisco Chronicle last week that she is prepared to intervene if the presidential race does not resolve itself by the end of June.

"I will step in," Pelosi told the paper in an interview. "Because we cannot take this fight to the convention. ... It must be over before then."

A senior Democratic aide in Congress also told CNN on Friday that Pelosi is already calling uncommitted superdelegates and pressuring them to back either Obama or Clinton by the end of this week. Pelosi is collaborating with Reid on the effort.

In an interview with a San Francisco radio station last week, Reid said he spoke to Pelosi and Democratic National Committee Chairman Howard Dean. "We all are going to urge our folks next week to make a decision very quickly," Reid said.

Throughout the process, Dean has been pressing for superdelegates to make up their minds after this week's contests.

Facing an insurmountable lead among pledged delegates, Clinton is now counting on the remaining superdelegates to push her over the finish line, a proposition her campaign admits is a tall order.

"Is the road steeper than it was several weeks ago?," Clinton adviser Harold Ickes remarked on CNN's "Late Edition" on Sunday. "The answer is yes."

Still, Clinton told reporters after her primary win in Puerto Rico on Sunday that given her support among key demographics in swing states, she has proved she will be a stronger nominee than Obama against John McCain.

"I think it's only now that we're finishing these contests that people are going to actually reflect," Clinton said on her campaign plane Sunday, referring to the uncommitted superdelegates. "Who's our stronger candidate? And I believe I am, and I'm going to make that case, and at some point it will either be accepted or it won't be, but I feel strongly about making it."

Clinton argued that even superdelegates who have committed to Obama are free to "change their minds" -- a suggestion the Obama campaign declined to comment on.

Despite the odds against her, Clinton continues to pick up support even as Obama grows his lead among superdelegates.

All About U.S. Presidential Election • Democratic Party