A 41-year-old California woman charged with heading an interstate prostitution ring here for 10 years that ended in February pleaded guilty yesterday to federal racketeering conspiracy and tax conspiracy charges.

Paulette B. Powell, who now lives in Sacramento, entered the pleas before U.S. District Judge Louis L. Oberdorfer. She faces up to 25 years in prison.

Assistant U.S. Attorney J. Michael Hannon said during the brief hearing that at least 40 clients of the prostitution ring and at least five other women, who previously pleaded guilty to lesser charges, had been expected to testify in the case.

Hannon said that the racketeering conspiracy began in September 1977 and continued through Feb. 2, 1987. Powell is accused of evading federal taxes from 1979 through 1982.

Sixteen persons were indicted in June for their alleged participation in the interstate prostitution ring, which prosecutors said used paging devices, operated out of luxury D.C. and area hotels, advertised in the Yellow Pages and accepted credit cards for payment. The clients were mostly out-of-town businessmen, according to court documents.

Also charged as one of the operation's kingpins was William J. Maiden, of 16707 Swanson Rd., Upper Marlboro, who for nine years has taught in the School of Architecture at Howard University. Maiden's wife Lynda was charged with being the day-to-day manager of the prostitution operation.

Powell is the former wife of Dennis Sobin, a sex-magazine publisher who favors legalizing prostitution. She is the mother of Darrin P. Sobin, who also was charged in the indictment.

The prostitution ring, which operated through a series of firms linked to Congressional Liaison Inc., operated out of 511 H St. SW and 729 and 729A Delaware Ave. SE, according to search warrants executed in April 1986.

According to court documents, women who worked for the prostitution ring were recruited with promises that they would receive legal help if they were arrested.

According to the indictment, the ring solicited much of its business through telephone book advertising. Women, who usually were called escorts, were dispatched to clients' addresses through paging devices. The women carried credit card imprinters to collect their pay, usually $120, of which they received $70, according to court documents.