The Securities and Exchange Commission yesterday filed a unique lawsuit against a Florida-based investment advisory firm alleging that it overcharged its clients -- two mutual funds -- for services rendered.

The case is sure to raise eyebrows on Wall Street because it marks the first time that the SEC has taken action against an adviser to an investment company for fees charged.

The suit, filed at U.S. District Court here, named American Birthright Trust Management Inc., a Palm Beach firm that advises two mutual funds, American Birthright Trust and Tax-Managed Fund for Utility Shares.

The suit also named ABTM's founder-president, Richard J. Sluggett, as well as Richard Freeman, executive vice president of ABTM, and six trustees and directors of the two mutual funds.

Without admitting or denying the SEC allegations, all defendants settled the complaint by agreeing to take certain actions.

As part of the court settlement, ABTM was ordered to pay $465,000 to the two mutual funds, an amount apparently equal to the overcharges alleged by the commission.

The six directors/trustees of the mutual funds resigned as part of the settlement. They are George V. Burget, Robert E. Davis, Edward K. Fehlig, Rolf Kaltenborn, Samuel V. Shannahan and Hugh W. Stone.

The new board is ordered in the settlement to review advisory fees paid by the two mutual funds, whose combined assets reportedly total about $200 million.

According to the suit, ABTM was charging the mutual funds many times what it was paying an investment adviser for servicing the two funds.

The SEC said that in 1978 the two mutual funds paid service fees to ABTM amounting to $1,298,012 and in 1979, $2,245,394.

Abtm, in turn, paid a hired investment "sub-adviser" named Arnold Ganz just $55,000 in 1978 and $70,000 in 1979, the SEC said.

Throughout 1978 and 1979, according to the suit, Freedman and Sluggett offered only "limited" advice to the funds which "did not result in significant investment research and analysis for the funds."

As a result, the SEC concluded, "ABTM has received substantial compensation for advisory services which Ganz actually provided."

In short, the SEC alleged that some of the investors' funds, which purportedly were being used to pay advisory fees, were actually up in the pockets of Freedman and Sluggett. Sluggett, in addition to being founder of ABTM, is also trustee or director of the two mutual funds.