MOSCOW (AP) _ The wife of American reporter Nicholas Daniloff said Monday that Soviet authorities plan to keep him in jail for a 10-day investigation before deciding whether to release him or charge him with spying.

Ruth Daniloff called the investigation ''a complete farce'' and said she feared her husband would be put on trial.

Mortimer B. Zuckerman, chairman of U.S. News & World Report, the weekly magazine that employs Daniloff, called the jailing ''a phony arrest based on contrived circumstances.''

Zuckerman flew here Monday from Washington and said he would meet with senior Soviet officials Tuesday to press for release of the 52-year-old newsman.

Daniloff has told his wife he was jumped by eight KGB agents Saturday after meeting a Soviet acquaintance who gave him a package later found to contain two maps marked ''top secret'' and photographs of Soviet military installations.

Mrs. Daniloff and the couple's 16-year-old son, Caleb, spent about an hour with him Monday in an annex of east Moscow's Lefortovo Prison.

U.S. Consul General Roger Daley accompanied them to Lefortovo but was not present for the meeting with Daniloff.

Daniloff was interrogated for four hours Saturday in Lefortovo. His wife said he was questioned again Monday, but she gave no details.

Outside the prison, Mrs. Daniloff told reporters her husband ''will be held for 10 days. ... (Then) they will decide whether they are going to release him or charge him.''

She said both Daniloff and KGB investigator Valery D. Sergodeyev mentioned the time limit. Whether the 10 days would be counted from his arrest Saturday was not clear, she said.

''I am very pessimistic because, you know, they found this incriminating information that was planted on him, so the investigation itself is a complete farce,'' Mrs. Daniloff said.

She said once the investigation is over, ''I think they will probably put him on trial. Unless something happens in between.''

In its Tuesday editions, The Washington Post quoted the Soviet Foreign Minister's chief spokesman as saying Moscow intends to try Daniloff.

The spokesman, Gennadi Gerasimov, was quoted as telling the Post in an interview that Daniloff has no diplomatic immunity. ''After an investigation, he will be put on trial,'' the newspaper quoted Gerasimov as saying.

In Washington, State Department spokesman Peter Martinez late Monday told The Associated Press the department would have no comment on the Post report.

Daniloff has suggested through his wife that his detention is a Soviet response to the Aug. 23 arrest in New York of Gennady F. Zakharov, a Soviet United Nations' employee charged with trying to buy U.S. secrets. Zakharov, who has no diplomatic immunity, is being held without bail.

Mrs. Daniloff said her husband was ''very subdued'' Monday but ''greatly heartened when I told him about the kind of press coverage he was getting.''

''He was concerned about being forgotten, and I said, 'Well, it's a big story.' And he said, 'You know it's a big story today, but maybe in two months time it will no longer be such a big story,''' she reported.

She said he told her that KGB photographers were present at his arrest, and also when the package was opened at Lefortovo.

Daniloff is allowed to exercise once a day in what she called ''a sort of cage'' on the prison roof and otherwise spends his time reading a Russian- language collection of works by French author Victor Hugo that was left in his 8-by-10-foot cell, she said.

With Daniloff in the cell is ''this character, (Soviet) physicist person,'' she went on. ''I think he (Daniloff) understands very well the role of this gentleman in the cell with him.''

Mrs. Daniloff said she did not expect to see her husband again until at least the end of the week.

She said he was particularly pleased to see Caleb, a high school junior who must return to class Wednesday at Northfield, Mass.

Caleb said he put meat, cheese and cookies in a package for his father, but was not allowed to not give him vitamin pills and aspirin.

''I was happy to see him, at the same time I was sad knowing that this was the last time I'd see him before I leave,'' the boy said.

Daniloff has been in Moscow 5 1/2 years and was to leave this week on a month-long trip retracing the steps of a Russian ancestor jailed in Siberia in 1825. He then was to return to the United States for reassignment.

Jeff Trimble, who arrived on Aug. 22 as Daniloff's replacement for U.S. News & World Report, said Zuckerman was to meet Tuesday with Kremlin U.S. expert Georgi A. Arbatov.

Trimble said Zuckerman also sought meetings with Foreign Minister Eduard A. Shevardnadze and others.

Asked about a possible Daniloff-Zakharov swap, Zuckerman told reporters at Moscow airport: ''Nick Daniloff should not become a pawn in that particular game that the Soviets are playing in the United States.

''I think it's just outrageous that somebody in the normal performance of his job becomes a pawn in whatever political games are being played.''