Four of the nation's largest oil companies agreed in court yesterday to clean up MTBE contamination in California caused by leaking gasoline storage tanks or face contempt of court penalties. The settlement, which will cover approximately 700 contaminated sites owned by Chevron, Shell, Texaco and Unocal since 1994, was signed in San Francisco Superior Court and could result in an outlay of millions of dollars in company cleanup costs...Superior Court Judge Stuart Pollak, who approved the settlement yesterday, praised it as a "sensible, very imaginative solution to the problem." But four oil companies -- ARCO, Exxon, Mobil and Tosco -- declined to settle the suit, and Pollak strongly urged them to meet with the court mediator to reach a similar agreement.