Creation of new money market mutual funds and restrictions on old ones were announced yesterday as the industry continued to react to controls by the Federal Reserve.

Meanwhile, fund operators were still trying to decide late yesterday whether to go to court in an effort to overturn the Fed's requirement of 15 percent reserves on additional assets acquired after March 14. Matthew Fink, counsel to the Investment Company Institute, a trade organization of mutual funds, said a decision was expected today.

Merrill Lynch's chairman, Donald T. Regan, announced his company would soon offer a new money market fund having an investment mix different from Merrill Lynch's Ready Assets Trust, the world's largest money market fund with $11 billion in assets. Dreyfuss Liquid Assets had previously announced it had filed an application with the Securities and Exchange Commission to open a Dreyfuss II Fund. Dean Witter also is filing to start a new fund.

These so-called "clone" funds, which wil pay investors a lower interest rate than the pre-March 14 parent funds, are the results of an SEC advisory warning the industry, in effect, that there would be less risk of disgruntled shareholder lawsuits if they protected the yields of prior investors rather than diluting them through the addition of new assets in comingled funds. Newly established funds are expected to yield up to 2 1/2 percentage points less than pre-March 14 funds.

Other companies have opted to limit existing funds, E. F. Hutton, which closed its Cash Reserve Management Fund on Monday, reopened it the next day with a cap of $100,000 a day on additonal deposits by individuals. However, new money, minus redemptions, would be held to the March 14 limit of $1.4 billion National Liquid Reserves has a similar plan. mGovernment Investors Trust will try to pay new investors different yields in the same fund. Fidelity Daily Income will disclose its plan today.

If the Investment Company Institute goes ahead with its suit, it is expected to plead that the Fed misused its authority under the Credit Control Act to require reserves on money market mutual funds.

In a recent letter to Fed chairman Paul Volcker, Senate Banking Committee Chairman William Proxmire "D-Wis.) stated the industry's case: "The purpose of the (act) is to control inflation generated by the extension of credit in an excessive volume. . . . Unlke the commercial banking system, money market funds have no substnatial capacity to expand the supply of credit. Indeed most of their funds are invested in (bank) or government obligations.

Proxmire also charged that the move would penalize small savers and would constitute "a back door form of Regulation Q on money market funds." (The administration has supported lifting of Regulation Q, which sets interest ceilings, from banks and savings institutions.)