THE INVESTIGATION of cocaine allegations against White House chief of staff Hamilton Jordan has now quietly expanded from New York to California, and the special prosecutor's office is looking for previously unidentified witnesses who attended an Oct. 22, 1977, party in Beverly Hills.

At least three of those potential witnesses, The Washington Post has learned, are young women who attended the party with Jordan and other Carter Administration insiders at the party.

One is a college girl who was only 18 at the time of the party. Another has been identified to The Post as a waitress who served members of Jordan's entourage lunch earlier in the day. A third, according to one source, is a blond from Las Vegas introduced during the evening only by her first name.

The women were never previously contacted by the Federal Bureau of Investigation because agents had never learned their names during a preliminary investigation.

The party's host, industrialist Leo Wyler, went on a CBS television evening newscast last September to say that Jordan and three other men had arrived at the party accompanied by "floozies" and that people at the party were talking about "hits" which he interpreted to mean the use of drugs.

The White House later produced other witnesses on CBS to refute Wyler's allegations that there were either "drugs" or "loose women" present during the evening.

The special prosecutor, Arthur H. Christy, when he expanded to California, exercised a broader mandate than the one originally recommended by Attorney General Benjamin R. Civiletti.

Last November, Civiletti had asked the federal court judges who appointed Christy to limit the inquiry to New York and allegations about Jordan's visit to Studio 54 on June 27, 1978.

But the judges instructed Christy to investigate not only the alleged incident at Studio 54, but "any other related or relevant allegation" that Jordan violated the federal law against possession of such drugs.

Former President Richard M. Nixon's new 15-room office suite in New York has a "motion detector" that sets off alarms if unauthorized persons enter his file room.

A General Services Administration spokesman said last week that the Secret Service paid for the alarm and for the wiring that connects it to their security office.

GSA billed the Secret Service $425 for installation.

A spokesman for the Secret Service said that "the GSA wasn't supposed to tell anyone that." The Secret Service has "no concern about the files," he claimed. In his words, "the alarm goes off as a security compromise indicator as opposed to protecting any papers."

In addition to the file room, Nixon's new space includes nine offices, a conference room, a reception room, a mail room and a $10,000 kitchen.

The taxpayers' bill for interior decorating came to $44,815. The annual rent, $68,000 comes out of his 1980 office budget allowance from Uncle Sam of $262.500.