By David Lawder

WASHINGTON (Reuters) - Republicans in the House of Representatives will take an election-year dig at top Democrat Nancy Pelosi in changes added to a fast-moving ethics bill, adding new curbs to prevent government officials from gaining special access to initial public stock offerings.

A senior House Republican aide said on Tuesday the so-called "Pelosi Provision" would strengthen the Stop Trading on Congressional Knowledge (STOCK) Act passed by the Senate last week.

The bill, scheduled for a House vote on Thursday, aims to prevent lawmakers from using inside knowledge gained through their positions to profit in the stock market by subjecting them to new trading disclosure requirements.

The provision, one of a number of changes drafted by House Majority Leader Eric Cantor, aims to shine a spotlight on Pelosi's husband's purchase of shares in the 2008 initial public offering by Visa Inc as Congress was considering new credit card regulations.

The CBS news show "60 Minutes" highlighted the transaction as one of several controversial trades by lawmakers in a piece last November that drew national attention to the profits generated by Congress' inside knowledge -- and sparked new support for a bill that had languished in the House for years.

Within two days of the Visa offering, the 5,000 shares purchased by Paul Pelosi had risen $20 each.

House Republicans widely described the addition as the "Pelosi Provision" on Capitol Hill, with specific references to the Visa transaction in the 60 Minutes piece.

"The Pelosi provision prohibits members of Congress, executive branch officials and their staffs from receiving special access to initial public offerings because of their position," the senior House Republican aide said.

SPECIAL ACCESS DENIED

Pelosi spokesman Drew Hammill declined comment until the House changes to the insider trading bill are released. "We look forward to reviewing to the text of the bill Leader Cantor is writing in secret," he added.

But Pelosi aides said that her husband, Paul, did not gain any special access to the IPO. He purchased them through his existing broker at Wells Fargo, one of the 41 banks that were underwriters in the $17.9 billion IPO, the largest in U.S. history.

The House Republican changes could add some partisan rancor to what has been an unusual display of support from both parties for the "clean government" measure in a deeply divided Congress. The Senate passed its version last week by a vote of 96-3.

Democrats also on Tuesday protested that Cantor's changes were being made behind closed doors without their input.

"How ironic. Insiders now appear to be writing a bill meant to ban insider trading," said Congressman Tim Walz, a Minnesota Democrat who had reintroduced a version of the STOCK Act last year.

At a news conference, Walz called on Republicans to "bring this dang thing out in the open."

Like the Senate bill, the House changes are expected to extend requirements that stock trades be disclosed electronically within 30 days to officials in the Executive Branch agencies and independent regulatory bodies.

But rather than forcing more than 300,000 lower-level employees as called for under one Senate amendment, the House version would limit this to about 30,000 higher-level officials.

Language of the Republican changes to the bill was expected to be released later on Tuesday.

(Reporting By David Lawder; Editing by Philip Barbara)