The Chicago Board of Trade said it will impose permanent daily price limits for its Major Market Index and Institutional Index stock index futures. MMI futures are based on a basket of 20 blue chip stocks that closely tracks the Dow Jones industrial index. II futures reflect movements in 75 major stocks widely held in large institutional portfolios. The indexes are key elements in some forms of computerized program trading, in which investors buy and sell the indexes and their underlying stocks in order to exploit price discrepancies. The 40-point MMI and 25-point II daily price limits will be effective from the opening of business today.