(Recasts first paragraph; adds Republican reaction, expert comment, paragraphs 8-9, 14-15)

By Susan Cornwell

WASHINGTON, Jan 30 (Reuters) - The White House pledged action against "irresponsible" bonuses for executives at bailed-out Wall Street companies as a Democratic senator unveiled legislation to limit their compensation to $400,000 a year.

Sen. Claire McCaskill proposed a law on Friday that would prevent executives from making more money than the U.S. president until their companies no longer rely on the $700 billion Troubled Asset Relief Program (TARP).

McCaskill, an early endorser of President Barack Obama's candidacy, gave an angry speech on the Senate floor in which she said an average of $2.6 million dollars had been paid in bonuses to executives from the first 116 banks that got money from the TARP rescue plan.

"I am mad," the Democrat from Missouri said. "We have bunch of idiots on Wall Street that are kicking sand in the face of the American taxpayer. ... They don't get it!"

At the White House, Obama's spokesman said the president's upcoming plan for financial stability also would address executive compensation and bonuses.

"I think you will see the president and his economic team outline a plan to deal with what he found irresponsible yesterday," Robert Gibbs told reporters. "Stay tuned, because something on that is coming soon." He declined to say more.

Obama on Thursday said recent Wall Street bonuses, given the current situation, were "shameful." His Democratic administration is working on options to stabilize the U.S. banking industry after various experts have said the $700 billion already allocated to TARP will not be enough.