Speaker Nancy Pelosi and top Democrats are making a last-ditch attempt to salvage a bill to renew expired surveillance tools Wednesday amid mounting opposition from Republicans and liberals in their own party, but it's still unclear whether the gamble will succeed.

Hours ahead of the scheduled floor vote, Pelosi and her top deputies were still whipping their members, with a growing number of progressives privately saying they would oppose the bill, according to people familiar with the discussions.

Pelosi told Democrats on a private caucus call Wednesday morning that they...