If the government has trouble keeping secrets, so do journalists.

The publication of Washington Post assistant managing editor Bob Woodward's book on William J. Casey's tour of duty at the Central Intelligence Agency was supposed to be kept under wraps as tight as some of the CIA's undercover operations. Its release was scheduled to begin today in The Post, Newsweek and other news publications around the country that had paid for serialization rights.

But late Friday, editors at U.S. News & World Report announced that they had obtained galleys of Woodward's book. Intent on scooping rival Newsweek as well as The Post, U.S. News issued a news release and a review/news analysis revealing some of the major disclosures about covert CIA operations contained in the book, "VEIL: The Secret Wars of the CIA, 1981-87."

Reports on the news analysis -- written by former Newsweek Washington bureau chief Mel Elfin, who is now director of planning at U.S. News -- were then carried on all three network television news shows, the news wires and in many of the nation's newspapers.

Most news organizations played up a hospital visit by Woodward to the dying Casey, in which Woodward asked whether he really knew about the Iran arms sales diversion to the contras. In the book, Casey nodded, and when Woodward whispered the question, "Why?" Casey responded, "I believed."

Asked yesterday whether he felt that was a definitive answer from Casey, Woodward said: "I've kind of gone back and forth on it. If you had seen it, you'd consider it definitive. But . . . it didn't go any further. It hangs there because it was a nod and because I couldn't follow up. To me personally, he was saying yes . . . . To not know would have been a denial of all that he was."

U.S. News editor David R. Gergen said yesterday that his staff had scrambled to find an advance copy, obtained galleys or page proofs "mid-week" last week, and began working on extracting some of its news in time for release Friday.

Gergen added that other news organizations have asked for copies of their galleys, and he has refused. He said that after writing their story, the editors locked the galleys in a "safe place" in the U.S. News offices in Washington.

Acknowledging that Elfin and other editors at U.S. News formerly worked at Newsweek, Gergen said that their copy did not come from Newsweek or The Post. (The Washington Post Co. owns Newsweek.) But he refused to say where it did come from.

Besides being excerpted in The Post and Newsweek, Woodward's book was sold in a series form to 46 other newspapers in the United States and Canada, including The Boston Globe, the Chicago Tribune, the Dallas Times Herald and The Miami Herald.

To maintain secrecy, review copies in this country went out only to The Post and Newsweek. The publisher, Simon & Schuster, was also under orders to keep the work hidden from competitors until excerpts had been printed.

Woodward's 511-page book is scheduled to be published Oct. 7, and 600,000 copies have been printed for the first edition.

At the Post, the early news reports on the book prompted a change in schedule, so that a news article by Haynes Johnson that was set for today's paper was moved to Saturday's editions. The Post's Saturday story focused on a Casey operation that circumvented normal CIA channels for secret operations in the Middle East.

The Washington Post Magazine today contains a Casey profile adapted from the book. And news excerpts begin today instead of Monday.

Several Post editors said they were surprised that the details of the book remained under wraps as long as they did. Some information began filtering out in Washington Friday because The Washington Post Magazine was inadvertently delivered early to some homes in the suburban area.

Gergen, obviously pleased with his magazine's score, said he was not surprised a news organization could not keep Woodward's book secret for so long. "News organizations aren't very good at managing news," said Gergen, who was President Reagan's director of communications from 1981 to 1984.

Colleagues said that when he was told that The Post's publishing schedule had been disrupted because a rival news organization had obtained a copy of his book, Woodward joked: "I've had it up to the keister with these leaks." He was alluding to a Reagan complaint about how the government also has trouble keeping secrets.