Ross Fields, the former American University student who went on to become a multimillion-dollar fight promoter under the alias of Harold J. Smith, was sentenced yesterday to spend 40 weekends in jail and work 1,500 hours in a hospital upon conviction on federal charges of falsifying passport information.

In Los Angeles, U.S. District Judge Manuel Real also put Fields on five years probation. He ordered him to report to jail June 27 for his first weekend behind bars.

Fields, 38, who ran track at American University in the early- and mid-1960s and went on to become a Washington area fight and concert promoter, is a defendant in a $21.3-million lawsuit filed by Wells Fargo National Bank charging that as chairman of Muhammad Ai Professional Sports Inc. (MAPS) he and others defrauded the bank of that sum.

The case is also under investigation by federal authorities, but no charges have been brought and Fields has maintained his innocence, contending that bank officials themselves were guilty of fraud.

As chairman of MAPS, Fields had taken the boxing world by storm in recent years, spending lavishly on fight purses and promotions. But that all collapsed after the filing of the lawsuit last January and he went into hiding for seven weeks.

In addition to the passport case, in which he was convicted of the filling out of a passport application under the false name of Harold J. Smith, Fields faces possible extradition to North Carolina on bad-check charges.

Federal prosecutors have described him as "a bunco artist" who traversed the country after leaving Washington in the early 1970s, leaving a trail of more than 100 bad checks in 30 states.

Fields said he felt the sentence was "very fair, just punishment" and that he has "no problems" with spending the weekends in jail.