“Poor Mexico! So far from God, and so close to the United States!” So goes a popular Mexican lament, true for more than a century-and-ahalf and still appropriate today. In recent years, however, important factors in U.S.-Mexican relations have altered sharply; and when President Reagan meets with Mexican President Jose Lopez Portillo and other American leaders in Cancun, Mexico, this October for a conference on world development, it is likely that a number of thorny issues will arise. What is unlikely is that they will result in any quick resolutions.