PHOENIX (AP) _ An interstate probe of computer hacking has uncovered losses that may reach millions of dollars and could be ''just the tip of the iceberg,'' federal law enforcement officials said Wednedsay.

No computer-crime arrests resulted, however, when 27 search warrants served in a dozen cities were served by 150 Secret Service agents and police on Tuesday, officials said. Three people - one each in Chicago, Los Angeles and Pittsburgh - were arrested for unrelated offenses, officials said.

Secret Service officials declined to release any specifics, including the number of people targeted, saying the two-year investigation, code-named ''Operation Sun Devil,'' was continuing.

The probe is focused on illegal entry into computer systems and unauthorized use of credit-card numbers and long-distance codes, said Garry M. Jenkins, assistant Secret Service director for investigations.

''The losses that we estimate on this may run to the millions of dollars,'' said U.S. Attorney for Arizona Stephen McNamee, who joined Jenkins and Arizona Attorney General Bob Corbin at a news conference.

''Most of you have been taking this as a game,'' Corbin told reporters. ''It is not a game. ... They're not all kids. They're adults, too.''

Much of the alleged loss stems from unpaid telephone and computer access charges, the officials said.

They said it was possible that hackers had gotten goods or cash through use of unauthorized credit cards, but could not cite any instance of it.

In addition to misuse of credit cards and phone lines, the hackers are believed to have gotten into computers that store medical and financial histories, the officials said.

The case ''appears to be the largest so far'' in the field, said assistant U.S. Attorney Tim Holtzen. However, it ''is probably only the tip of the iceberg'' when it comes to computer crime, he said.

Statements from the Secret Service and the Justice Department gave conflicting information on the number and locations of the cities where searches were made.

In addition to searches in or near Phoenix, there were searches conducted this week in or near Chicago; Cincinnati; Detroit; Los Angeles; Miami; Newark, N.J.; New York City; Pittsburgh; Richmond, Va.; Plano, Texas, and San Diego.

Also listed in some of the statements were San Jose, Calif.; Saginaw, Mich.; San Francisco and Tucson. Officials said they were unable to explain the discrepancies.

Documents on the search warrants will be sealed pending further investigation, assistant Attorney General Gail Thackery said.

Under new computer crime laws, the Secret Service has jurisdiction to investigate allegations of electronic fraud through the use of access devices such as credit-card numbers and codes long-distance companies issue to individual callers.

Defendants convicted of unauthorized use of such ''access devices'' can be sentenced up to 10 years in prison if they commit fraud of more than $1,000, according to the law.

A similar investigation supervised by federal prosecutors in Chicago has resulted in several indictments.