By Sarah N. Lynch

WASHINGTON, Feb 19 (Reuters) - Democratic Senator Elizabeth Warren's strong criticism of U.S. financial regulators last week has inspired a liberal political action committee to launch an online petition urging the Securities and Exchange Commission to take more Wall Street banks to trial.

The petition, introduced by the Progressive Change Campaign Committee on Sunday, came a few days after the freshman senator from Massachusetts made her debut on the influential Senate Banking Committee.

In an exchange that drew applause from protesters in the audience, Warren demanded to know the last time banking and financial market regulators had taken Wall Street banks to trial, as opposed to settling the cases.

"I'm really concerned that too-big-to-fail has become too-big-for-trial," Warren told the regulators.

After the hearing, Warren's staff posted clips of the exchange on YouTube that soon went viral. So far, three separate postings of a version of the clip have collectively received more than 1 million hits.

The Progressive Change Campaign Committee, which helped Warren raise more than $1.6 million in her 2012 campaign to defeat Republican incumbent Scott Brown, posted its petition to the SEC on Sunday.

The petition, which urges the SEC to end its practice of "too big for trial," garnered more than 10,000 signatures in the first 24 hours, a number that has climbed to more than 16,000, according to Matt Wall, a spokesman for the group.

Wall said he expects the group to deliver the petition to the SEC in the "near future."

Last week SEC Chairman Elisse Walter told reporters after the hearing that she does not believe the agency should bring banks to trial if it can obtain relief through a settlement.

She added that the SEC, whose budget must be approved by Congress, needs to take account of its resources in deciding which cases to settle and which to take to trial.

On Tuesday, SEC spokesman John Nester said the agency is "fully prepared to go to trial every time" it files a suit.

However, he added, "There's no reason under our authority to delay justice and financial relief for investors when we can get it all without a trial."

In a statement, a spokesman for Senator Warren said she "believes that everyone has a stake in an honest system where people are held accountable if they break the rules."

"She has fought for a long time to make sure that lenders that provide real value to their customers aren't forced to compete with institutions that build their profit models on deceptive or abusive practices," the spokesman added.

SETTLEMENTS UNDER ATTACK

The SEC's settlements have been under the heavy scrutiny in recent years.

The agency is currently appealing a judge's rejection of a proposed $285 million settlement with Citigroup. In refusing to approve the accord, the judge challenged the SEC's practice of letting companies settle without admitting or denying allegations.

Many of the SEC's most notable cases against banks arising from the financial crisis have resulted in settlements.

One prominent settlement was a $550 million deal with Goldman Sachs Group Inc over allegations it misled investors in a subprime mortgage product. Goldman initially contested the allegations, but it later agreed to settle for what the SEC said was 35 times the amount the bank stood to make on the offering.

When the SEC has taken banks to trial, it has been met with mixed results.

Some successes included one last week when the SEC won a $110,500 judgment against Morgan Keegan in connection with its sale of auction-rate securities - a case that had been going on for about three and a half years. A court ruled that Morgan Keegan was negligent, but it did not find that the firm intentionally defrauded investors.

However, other high-profile cases have not been decisive victories.

In November, a jury rejected civil fraud charges against Reserve Primary Fund founder Bruce Bent, whose money market fund "broke the buck" during the financial crisis after its heavy exposure to Lehman Brothers prompted an investor sell-off.

His son, Bruce Bent II, was cleared of knowingly violating securities laws but was convicted on one count of negligence. Two of the Bents' companies were also found liable on some charges.

In one of the biggest blows to the SEC, a jury in July threw out a civil fraud case against former Citigroup manager Brian Stoker over allegations he misled investors in a pool of mortgages.

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