Harvard Law School had to do without "L.A. Law"-yers Harry Hamlin, Michelle Green, Richard Dysart and Blair Underwood (a.k.a., respectively, Michael Kuzak, Abbie Perkins, Leland MacKenzie and Jonathan Rollins) because the university could not afford to buy them first-class airline tickets from Los Angeles to Boston. The dispute arose two weeks ago, according to David VanCleve, president of the Harvard Law School Forum, sponsor of the "An Evening with L.A. Law" forum scheduled for Wednesday. VanCleve said school policy calls for providing coach air fare for forum participants, rather than the first-class tickets that a spokesman for the show told him were mandated in the quartet's Screen Actors Guild contracts. "We discovered it would be prohibitively expensive to bring them out, so it was with great reluctance we decided to cancel," he said. First-class air fare would cost about $8,500, rather than the $2,000 to $3,000 the forum had planned to spend on coach fare, VanCleve said. "L.A. Law" spokeswoman Lark Zonka said an attempt had been made to get the balance of the fare from producer 20th Century Fox, "but we don't have the money for that kind of thing."