A convicted sex offender and his wife have pleaded guilty to kidnapping and raping a California girl in a surprise plea deal that will spare their victim and the two daughters she had during her 18 years of captivity from taking the stand at a trial.

A lawyer in the case of a Northern California girl held captive in a backyard compound for 18 years said he expects defendant Phillip Garrido to plead guilty to all charges and his wife to go to trial unless she gets a better plea deal.

A couple charged with kidnapping an 11-year-old girl and holding her captive for 18 years have made full confessions, a defence lawyer said.

Jaycee Dugard, the girl held prisoner in California for 18 years, will be spared from giving pre-trial evidence against her alleged captors.