President Reagan has "full confidence" in his deputy national security assistant, Thomas C. Reed, a White House spokesman said yesterday.

Over the weekend, Reed, whose 1981 stock dealings are under investigation by a federal grand jury in New York, characterized a congressional review of his case as "political fun and games in Washington."

A White House official said yesterday, however, that senior administration officials discouraged Reed from taking this approach after he made the comment.

White House spokesman Larry Speakes said questions about Reed's financial dealings would be handled by national security affairs adviser William P. Clark.

Speakes said the National Security Council, where Reed is designated as a special assistant to the president, is a "separate entity" within the executive office of the president.

Therefore, Speakes said, an issue concerning NSC personnel is "a matter which the NSC counselor is looking into."

Reed, who has not been available for comment on the grand jury investigation, made his comment about the congressional inquiry in Las Vegas, where he delivered a speech Saturday.

Clark will meet with Rep. John D. Dingell (D-Mich.) later this week to discuss Dingell's request that the NSC turn over its security file on Reed, officials said. Dingell is looking into the Securities and Exchange Commission's investigation of Reed and the NSC's security clearance procedures in Reed's case.

The grand jury investigation grew out of a December, 1981, SEC consent order Reed signed after a single stock transaction netted him $427,000 on a $3,125 investment in the stock options of Amax Corp. Reed's father sits on the Amax board of directors.

The SEC alleged that Reed had traded on inside information in the deal and required Reed to set the windfall aside to pay the claims of investors hurt by the deal.

The SEC investigation determined that Reed had signed other people's names to documents in the stock transactions and backdated the documents to make it appear that the $427,000 windfall was spread among eight different people.

Reed said his motive was to make a gift out of the proceeds. SEC officials have told House investigators that Reed complained through his lawyers in 1981 that publicity associated with the SEC investigation had cost him a senior post in the Reagan administration and the job of president of Pan American World Airways.

Meanwhile, White House officials have said in interviews that Reed's June, 1982, appointment to the NSC staff and subsequent security investigation were rushed at Clark's insistence. They say that Reed was given the title of special assistant to the president because the title of "consultant" did not seem sufficient for his duties.

One official said Reed was not screened by White House counsel Fred F. Fielding's office, but when an FBI background report mentioning the SEC case was sent to Fielding's office as a courtesy, Fielding's staff suggested that the NSC look into the matter.

NSC security chief Richard C. Morris met with SEC officials.

SEC enforcement officials have told House subcommittee investigators that Morris questioned them on whether they thought Reed had lied during the investigation.

The SEC officials reportedly urged Morris to review their investigative summary, but Morris didn't do it, subcommittee investigators said. An NSC spokesman, Capt. Robert Sims, said during the weekend that Morris read a copy of Reed's sworn testimony as part of the background check.

Sims said yesterday that Reed is no longer being paid as a $210-a-day consultant to the NSC because he recently exceeded the 120-day annual limit on such arrangements.

"His work currently is for free," Sims said, adding that Reed could draw consultant's pay again in May.

Dingell aides said there is some question of whether Reed can function as a government employe or consultant without being on the federal payroll.

When he was receiving a consultant's pay, Reed was listed as a GS-15, step nine employe, one step below the level that requires filing financial disclosure statements.

Subcommittee investigators also said yesterday that Energy Department security personnel last week were denied access to Reed's security file by an unidentified White House official who said there was an ongoing investigation.

When asked yesterday if there were a new White House inquiry of Reed, Speakes replied, "Not specifically . . . . As yet, there have been no specific new charges."

NSC officials renewed Reed's top-secret "Q" clearance for nuclear materials last October without providing the DOE officials responsible for granting the clearances any information about the SEC case.