The National Academy of Sciences said that a newspaper advertisement claiming the academy had cleared Continental Oil Co. of charges that it withheld natural gas two winters ago is misleading and inaccurate.

"We never investigated if gas was held back or why it was held back," an academy spokesman said. "We also were not looking to fix blame, which the ad in question clearly implies."

On Feb. 16, Continental Oil took a full-page ad in The Washington Post calling attention to eight news stories that said the Interior Department was investigating whether natural gas producers withheld gas from production during the gas shortage two winters ago.

A headline in the ad read: "A year ago,you couldn't miss the charges." Below that headline read another: "But you probably missed the follow-up."

The "follow-up" was a study done by the National Academy of Sciences for Interior Secretary Cecil D. Andrus to find out if gas had been withheld. The copy in the ad states the following:

"The Academy has now completed its investigation of the fields in question operated by Conoco. It concludes that these fields have been producing gas 'as fast as possible.' Secretary Andrus accepted this report clearing Conoco and issued a news release to that effect.

"But it is an unfortunate fact of life," the ad goes on, "that charges make headlines and exoneration gets lost in the inside pages - if it is mentioned at all. While the Washington Post featured the original charges on the front page, it chose to ignore the follow-up story on Conoco."

The ad's appearance prompted Accuracy in Media, a Washington-based organization that monitors press performance, to question why The Post had not followed up the story. In looking into it, The Post found what appeared to be inaccuracies in the ad.

The ad said Conoco had been cleared of any charges that it withheld gas, which the academy says is not true. The academy says it never investigated whether gas was held back, only whether gas fields in the Gulf of Mexico could economically produce more gas than they had.

The academy studied six gas fields in the Gulf of Mexico, none of them the fields operated by Conoco that had been questioned by Interior Secretary Andrus. Exoneration of any charges was "impossible" under those circumstances, the academy spokesman said.

Finally, the academy said it never concluded that the fields had been producing gas "as gast as possible," the languagee used in the ad. The academy concedes that in its first report on two of six fields it studied it said there "were no opportunities on increasing production."

In a letter to Accuracy In Media's Reed C. Irvine, Conoco VIce President Edward J. Mulligan apologized for the ad's use of "as fast as possible." Mulligan said the quote had been "mistakenly" taken from a story in The Wall Street Journal that used the same language.

In letters to Andrus, Conoco Chairman Howard W. Blauvelt denied that Conoco oever withheld gas from production in any of the fields it operates in the Gulf of Mexico.

"Conoco has undertaken a vigorous natural gas program," Blauvelt said, "which has succeeded in reversing the declining trend of our U.S. gas production."