CBS News, joining ABC and NBC, announced yesterday that it will give the Justice Department access to hours of videotape taken during coverage of the hijacking of Trans World Airlines Flight 847 last month.

In a statement released after three days of discussions with department lawyers, CBS agreed to allow the government access to tapes it aired as well as those it did not, citing "the unique circumstances" surrounding the hijacking and "longstanding" network policies allowing release of material not broadcast if it is "essential to the investigation of crimes involving threats to human life."

Asked yesterday why CBS waited two days after ABC and NBC agreed to allow government access to their hijacking tapes, Ann Morfogen, CBS' director of communications, said the network feared that such an agreement would cause problems for television crews in the field.

She added that CBS lawyers and executives wanted to narrow the focus of the government's demands, "and we believe we did do that in some degree."

"It's also terribly important to sit down and discuss it, and not plunge in willy-nilly without thinking it through," she added.

On Tuesday, the Justice Department issued subpoenas to the major networks as part of an effort to identify and charge the three original hijackers of Flight 847 with the murder of one American passenger, Robert Dean Stethem of Waldorf, Md., and the 17-day confinement of 39 others.

A department spokesman said yesterday that CBS' agreement was similar to that obtained from the other networks. "The bottom line is pretty much the same," the spokesman said.

At Cable News Network headquarters in Atlanta, where the subpoena was not served until Thursday, officials withdrew their earlier statement that they would cooperate fully with the government, saying they wanted to reassess their position.

CNN spokesman Judy Borza said yesterday that the network's attorneys will continue discussions with Justice Department officials Monday on a way to comply with the subpoena while trying to "maintain our First Amendment privilege."

Asked what she meant in reference to a constitutional privilege, Borza said: "I'm not going to reword that -- no."