A federal grand jury in New York is investigating whether Thomas C. Reed, the deputy assistant to President Reagan for national security affairs, violated criminal law in the way he parlayed a $3,000 stock option investment into a $427,000 windfall in 1981.

In addition, the chief counsel of a House subcommittee alleged yesterday that the Securities and Exchange Commission "took a dive" in its 1981 investigation of Reed, who settled the SEC case without admitting wrongdoing while pledging not to use inside information to purchase stock in the future. Reed's $427,000 windfall was put in a fund by the SEC to reimburse other investors.

The chairman of the House subcommittee, Rep. John D. Dingell (D-Mich.), has asked the White House to turn over its security files on Reed so the subcommittee "can look at how the National Security Council staff evaluated the SEC matter when they gave Reed clearances and put him in one of the most sensitive positions in the government," according to a subcommittee aide.

A subcommittee source also said NSC officials last October requested from the Energy Department a top-secret "Q" clearance for Reed to deal with sensitive nuclear weapons information, but didn't tell Energy Department officials about allegations involved in the SEC investigation. Those allegations, according to the SEC case file, included signing the names of other people on stock brokerage forms, using various styles of handwriting to do so, and backdating them to make it appear that the windfall had been spread among eight people.

Reed, who has repeatedly denied any wrongdoing, had said he signed the names because he intended to present the proceeds of the stock transaction as gifts to friends and employes. He could not be reached for comment yesterday.

Reed, 48, a former Air Force secretary, businessman and fund-raiser for President Reagan's 1980 presidential campaign, was first hired by national security affairs adviser William P. Clark as a consultant on the National Security Council in January, 1982.

Last June Reed was named a special assistant to the president under Clark. Reed also is vice chairman of the presidential commission studying possible basing plans and alternatives for the MX missile.

The chief of security for the NSC, Richard Morris, reportedly was not aware of the New York grand jury investigation of Reed until subcommittee investigators told him about it Wednesday. The New York investigation apparently has been under way for a number of weeks.

During its 1981 investigation, the SEC probed whether Reed traded on inside information when he purchased options on Amax Corp. stock in March, 1981, at a time when Amax was discussing a merger proposal from Standard Oil Co. of California, the third largest U.S. oil company.

Reed's father was on the Amax board of directors, and telephone records subpoenaed by the SEC show a series of calls between Reed and his father just minutes before Reed called his broker to place orders. Another Amax director testified in the SEC case that Reed called him and specifically asked "what was likely to happen in the Amax-SoCal situation," according to SEC records.

Securities laws prohibit stockbrokers and purchasers from taking unfair advantage--such as from insider information--to trade in the securities of publicly held companies.

On March 4, 1981, the day before the Amax merger bid was announced, Reed purchased $3,125 worth of options to purchase 50,000 shares of Amax stock. Under the speculative terms of the options, the transaction would only pay off if the price of Amax stock rose dramatically. And it did.

On March 5, the merger bid was made public. By March 6, Amax stock had leaped from $20 a share to $58 a share, and Reed had made $427,000 in 48 hours.

Reed has described the SEC findings as "bizarre coincidence" rather than evidence of anything illegal.

John S. Martin Jr., U.S. attorney for the Southern District of New York, said yesterday that his office "is in the preliminary stage of investigation to determine what further action should be taken . . . in the insider trading case."

Martin said that he "normally does not confirm" the existence of ongoing investigations, but made an exception in Reed's case "given the public attention, given the public SEC proceeding and his position in the government."

Michael F. Barrett, chief counsel to the House Energy and Commerce subcommittee on oversight and investigations, said his staff has reviewed the SEC files of the Reed investigation. "They show how the SEC staff took a dive," he said.

SEC officials have in the past denied that Reed's case received special treatment.

According to a subcommittee source, Morris, the NSC's security officer, told the subcommittee that the SEC files had been reviewed in detail before Reed received his White House appointment. The subcommittee staff determined that no one from the NSC had checked out the file, and Morris later said that he had not read the file, according to the source. Morris could not be reached for comment.

Last December, when the self-styled citizens' lobby group Common Cause published a detailed account of the SEC case against Reed, based on records obtained under the Freedom of Information Act, White House spokesman Larry Speakes told Common Cause staffer Julie Kosterlitz, "All relevant factors concerning these activities were taken into consideration and thoroughly examined by the NSC staff before Mr. Reed was designated as special assistant to the president."

Although Reed holds a senior position on the White House staff, he is listed in government records as a consultant to the Defense Science Board, detailed to the White House at a grade of GS-15, step nine. This is one step below the pay level that requires the filing of financial disclosure statements available for public inspection. CAPTION: Picture 1, THOMAS C. REED . . . $ 3,000 grew into $ 427,000; Picture 2, REP. JOHN D. DINGELL . . . wants files from White House