STEVE RACKLIFFE, who teaches turf-grass science at the University of Connecticut, said the first step to a lush lawn is proper seed selection. Evaluate how much sun the lawn gets, whether the area seems prone to particular diseases or insects, and the amount of wear the lawn will get, and generally be realistic about your expectations for the lawn, given those conditions. For a showcase lawn, he said, use a blend of Kentucky bluegrass. ''It'll give you that manicured look, and it has good wear tolerance,'' he said, ''but it doesn't do well in shade and has a higher fertility need and moisture need than other grasses.'' In other words, be prepared to spend some time and money to keep this lawn green. [ABSTRACT FROM AUTHOR]