President Reagan is planning to name an interagency committee to develop an administration consensus on how to avoid another stock market crash, a White House official said Tuesday.

It's not another study; the studies have been done, the official said. Instead, he said, the group would pull together the ideas of various studies already completed and then develop a consolidated position.The group will be headed by Treasury Secretary James A. Baker III and include officials from the Federal Reserve Board, the Securities and Exchange

Commission and the Commodity Futures Trading Commission. Its report will be due within 60 to 90 days.

Studies on the crash have been produced by a presidential task force headed by former Sen. Nicholas F. Brady, as well as by the SEC, the CFTC and markets.

We've been looking at these reports and each of them is a little different, said the official, who declined to be identified. The idea of this group is to decide what can be done . . . to reach a consensus among the regulatory agencies.

The official said that while legislative action may be needed eventually, the main goal will be to see what they (the regulatory agencies) can do under existing authorities.

Wendy Lee Gramm, the new CFTC chairman, made it clear in a speech at the Futures Industry Association's annual meeting in Boca Raton, Fla., last week that she intends to defend her agency's regulatory authority over stock index futures.

Some studies, notably the Presidential Commission on Market Mechanisms, advocated that a single federal agency, such as the Federal Reserve System, regulate aspects of both stock index futures and the stock market.

Ms. Gramm strongly endorsed the current regulatory structure, saying it does not require a major overhaul.