UKIAH, Calif. (AP) _ A lawyer who had been missing for a month after being indicted on federal fraud charges was arrested trying to cross the border from Arizona into Mexico, officials say.

Patrick M. Finnegan of Ukiah is accused of concealing about $190,000 in legal fees after filing for bankruptcy and then going on a spending spree that included a Jamaican vacation.

He was arrested Monday by U.S. Customs agents at the Nogales crossing who ran a computer check that disclosed the outstanding federal warrant, said Assistant U.S. Prosecutor Peter Robinson in San Francisco.

Finnegan was taken before a U.S. Magistrate in Arizona late Monday and bail was set at $100,000.

Robinson said Finnegan will be returned to California immediately if the lawyer agrees to waive an ''identity'' hearing.

''All we have to do is prove Finnegan is who we say he is,'' said Robinson. ''If he balks, it may takes up to 10 days to get him back here.''

Finnegan and Christine Petersen were indicted last month by a federal grand jury in San Francisco on eight counts of bankruptcy and mail fraud. They failed to up for arraignment on July 22.

Finnegan's federal problems stem from a bankruptcy action filed in late 1984.

Robinson claims that Finnegan, despite being in bankruptcy and with the help of Petersen, took in two checks totaling $190,000 in attorneys' fees and spent much of the money during the next nine months.

None of the money, nor periodic financial reports required by the federal bankruptcy court, were disclosed to authorities, Robinson said.

Robinson said that if convicted on the charges, Finnegan and Petersen each face a maximum prison sentence of five years plus a possible $250,000 fine on each of the eight counts.