* Reserve Primary operators accused of deceiving investors

* SEC cites failure to disclose Lehman holdings

* Reserve Management says to defend itself vigorously

* SEC: seeks to expedite distribution of fund assets (Adds statement from independent trustees of Reserve Fund, details on lawsuits, background on money fund industry)

By Martha Graybow and Rachelle Younglai

NEW YORK/WASHINGTON, May 5 (Reuters) - The pioneer of the money market mutual fund, Bruce Bent Sr, was charged with fraud by U.S. regulators on Tuesday over accusations he deceived investors into believing his flagship fund was safe before it "broke the buck" last year.

The civil charges against the veteran investor, his son and their investment company come eight months after the Reserve Primary Fund, brought down by the bankruptcy of Lehman Brothers Holdings Inc, halted redemptions and sparked a run on money-market funds.

The collapse of the once $62 billion fund helped accelerate the global financial crisis last September and triggered a guarantee program by U.S. authorities to prevent a massive outflow from money funds.

The fund is being liquidated and its collapse has spurred numerous lawsuits. Its demise has been a stunning turn for Bent, who regulators called "a longtime advocate of the safety and stability of money market funds."