WASHINGTON — A national infrastructure bank that would entice private investors into road and rail projects could be a major part of the jobs package that President Barack Obama hopes will finally bring relief to the unemployed.

The White House hasn’t divulged the contents of the package that Obama is to unveil in an address to a joint session of Congress next week. But the president has pushed the idea of an infrastructure bank in recent speeches and has praised Senate and House bills that create such a government-sponsored lending institution.

Whether the bank, which would need time to organize, could have any real impact on the jobs situation in the coming year — and particularly before the November 2012 elections — is in dispute.

Obama seems to think it would.

“We’ve got the potential to create an infrastructure bank that could put construction workers to work right now, rebuilding our roads and our bridges and our vital infrastructure all across the country,” he said at a July news conference.