PORTLAND, Ore., Aug. 27 — Susan Murphy, 34, an associate of convicted mass murderer Charles Manson, and Diane Louise Ellis, 33, were taken into custody Thursday evening in Portland, the FBI announced.

The women, who escaped 13 days ago from a federal prison in Los Angeles, were arrested without incident by two FBI agents at a downtown intersection.

They were taken to the Multnomah County Courthouse jail. They will go before U.S. Magistrate George E. Juba today.

Officials said agents in cars and on foot patrolled downtown Portland during the afternoon and early evening because of information, on which the FBI declined to elaborate, that the women might be found there.

The FBI reported earlier Thursday that the women were believed to be driving through Oregon en route to Canada. They were believed to have left Philomath, Ore., Tuesday afternoon in a cream-colored Ford Maverick with California or Nevada license plates.

Miss Murphy was spotted in the car by an agent involved in surveillance in Portland and additional agents were called. They arrested the women when Miss Ellis walked up to the car, an FBI representative said.

The women overpowered a female guard at the Terminal Island federal prison facility on Aug. 14, taking the guard’s car and fleeing north to San Francisco.

Miss Murphy, a fringe follower of Manson, was serving a five-year sentence for conspiring with Manson cultist Sandra Good to mail threatening letters to businessmen they accused of polluting the environment. Both women were friends of Lynette “Squeaky” Fromme, who is serving a life sentence after being convicted of trying to kill President Ford.

Miss Ellis was imprisoned on parole violations following a bank robbery conviction. FBI agents raided an apartment in San Jose, Calif., early Wednesday and failed to find the fugitives but arrested the occupant, Pamela J. Bailey, 27, and charged her with harboring Miss Ellis.

Neighbors of Miss Bailey identified Miss Ellis as one of two women seen at the apartment as late as last Sunday. The second woman was not positively identified.

Miss Murphy, nicknamed Heather, lived in Sacramento with Miss Good and Miss Fromme, all professed followers of Manson. He is serving a life term for the 1969 slayings of actress Sharon Tate and six other people during a two-night murder spree.