* Senate postpones procedural vote on startups bill
* Export-Import Bank provision draws opposition
* Senate Democratic aides expect bill to advance Wednesday
* Critics say bill erodes investor protections
By Sarah N. Lynch and Alexandra Alper
WASHINGTON, March 20 (Reuters) - The U.S. Senate on Tuesday postponed a vote to advance a White House-backed bill to boost small business growth as some Republicans objected to an addition to the measure that would renew the Export-Import Bank's charter.
The bill is still expected to advance on Wednesday, Senate Democratic aides told Reuters.
Some said they expect it will pass the 60-vote threshold needed to pave the way for final passage, although one aide predicted the vote could be close.
The legislation had been on a fast track for approval in a rare showing of election-year bipartisanship, with both parties eager to be seen supporting efforts to bolster economic growth. The measure already passed the House earlier this month with overwhelming bipartisan support.
Senate Democrats had wanted to attach a provision that would reauthorize the Export-Import Bank. Some House Republicans have opposed it because of the government agency's use of taxpayer-backed loans to finance exports.
Republicans killed the Export-Import Bank measure in a procedural vote on Tuesday, angering Democrats and prompting Senate Majority Leader Harry Reid to call a brief time-out.
"Today, Republicans voted against an overwhelmingly bipartisan measure that would have supported more than 300,000 American jobs simply to provide cover for Tea Party extremists in the House," Reid said in a statement after postponing the vote and calling a party meeting.
"Once again, Republicans are manufacturing a fight instead of working with Democrats on bipartisan solutions to create jobs."
The legislation has been labeled by some of its backers as a way to help create jobs, and it is also supported by some major financial industry players including the New York Stock Exchange .
It has fallen out of favor with some Senate Democrats, however, who fear the bill relaxes too many securities regulations and puts investors at risk.
"Just at a time when investor confidence is increasing, where jobs are being created in the country, why would b e going to such a far-reaching bill?" said Louisiana Democrat Mary Landrieu.
Landrieu, along with Senators Jack Reed and Carl Levin, had tried unsuccessfully on Tuesday to advance a measure that would rewrite the bill to include more investor protections.
The amendment was easily defeated in a procedural vote after failing to win a two-thirds majority.
Among federal and state regulators and investor and consumer advocates weighing in with concerns, SEC Chairman Mary Schapiro had told lawmakers she feared that the House-passed version of the bill would exempt too many companies from important investor protections and also chip away at the firewalls in place to reduce conflicts of interest between investment bankers and research analysts.
Ahead of the vote, at a securities industry conference in Miami on Tuesday, Schapiro said she thought the proposed changes by Democrats would help address many of her fears about the bill.
"I think they help in a number of areas and I think that the Senate substitute version addresses some of the issues that I was most concerned about," Schapiro said, according to a transcript of her conversation provided by an SEC spokesman.
If the Senate passes the bill this week, it would likely lack the investor protections that Schapiro has called for.
Senate Democratic aides complained privately on Tuesday night that the Obama administration was too quick to endorse the House bill without thoroughly reviewing its impact.
Some have also been annoyed that Reid decided to bring the House bill to the floor without letting the Senate Banking Committee vet the bill first.