WASHINGTON  Perhaps the last best hope of Democrats to pass legislation aimed at creating jobs before the November elections seemed to be crumbling in the Senate on Wednesday as Republicans signaled that they would block a bill to expand government lending programs and grant an array of tax breaks to small businesses.

Wrangling over the small-business measure began in earnest after Senate Democrats, breaking a two-month partisan logjam, finally succeeded in winning an extension of unemployment insurance. The vote was 59 to 39, with two Republicans joining Democrats in support of the extended benefits, which are retroactive to June 1. One Democrat, Senator Ben Nelson of Nebraska, voted against it.

Shortly after the vote, the majority leader, Senator Harry Reid, turned to the small-business bill, one of the few items left on the Senate’s dwindling agenda before the August recess. Indeed, it had been on the floor intermittently over the last several weeks, only to be pulled to make way for other legislation including the extension of unemployment insurance.

But with some Democrats viewing the small-business bill as critical to their political prospects in November, Senate Republicans were not about to let it through easily, and have insisted on a chance to offer amendments.