WASHINGTON  It was a telling glimpse into the state of mind of rattled Senate Democrats.

Worried that they were going to be skewered for pushing a jobs bill that was stuffed with business tax breaks and pork, Senator Harry Reid, the majority leader, pulled the plug Thursday on a rare bipartisan proposal, gambling both with the party’s best chance of posting a needed legislative win as well as with President Obama’s new push for cross-party cooperation.

The surprise move by Mr. Reid, partly in response to fears from lawmakers that they were going to take a pummeling on cable news, has put the future of the jobs legislation in question and showed how the criticism heaped on their health care plan and the loss of the Massachusetts Senate seat have put Democrats in a protective crouch.

At the same time, Mr. Reid’s gambit puts pressure on Republicans to back elements they had already endorsed as part of the broader package, rolled out by top Democrats and Republicans on the Finance Committee, a note the White House sounded Friday.

“I think the legislation that Senator Reid will move when the Senate comes back into town will garner bipartisan support,” said Robert Gibbs, the White House spokesman.