By Svea Herbst-Bayliss

BOSTON, July 14 (Reuters) - A crackdown on rumor-mongering by U.S. securities regulators is likely to see many in the financial markets take a lot more care about how they pass on both serious views and scuttlebutt, at least for a while.

The big fear is that regulators will show up at hedge funds and brokerages, armed with subpoenas, demanding trading, phone and e-mail records to determine if any of them are to blame for declines in the shares of major financial companies such as Lehman Brothers Holdings Inc LEH.N.

"This is a world where people are blunt, and we have all called companies 'trash' before," said one hedge fund manager who asked not to be identified so he could speak freely. "But in this environment, where it is all about appearances, we are going to have to be a lot more careful."

The crackdown by the U.S. Securities and Exchange Commission (SEC), announced on Sunday, is an attempt to put an end to rumors that could threaten the stability of U.S. financial institutions.

The SEC said regulators would immediately examine whether broker-dealers and investment advisers have controls to prevent the spread of false information and any related market manipulation.

Some bankers and columnists have blamed rumors for the collapse of investment bank Bear Stearns and for the 40 percent slide in Lehman shares this month.

Speculators are also being blamed by politicians and some business leaders, including people in the airline industry, for sending oil prices to record highs.

"In the short term this will scare some of the folks who are small players," said Jon Najarian, a founder of Web information site Optionmonster.com. "True enforcement and not just talk could be a catalyst for a turnaround in both sentiment and the markets."