James Lassart, head of the federal drug prosecution team in Northern California and the Pacific Northwest, is resigning next month to enter private law practice. In 1983, Lassart became the first coordinator of the regional drug task force, which combines five federal agencies to tackle major drug organizations. The resignation was announced by U.S. Atty. Joseph Russoniello, who said Lassart's "dedication to duty and to the responsibility of drug enforcement have been extraordinary." Lassart, who had served along with Russoniello in the San Francisco district attorney's office, became an assistant U.S. attorney in 1981. He will join a San Francisco firm specializing in business law. Russoniello said the new coordinator will be Steve Graham, one of seven lawyers on the current task force.