A Justice Department spokesman last night defended the Reagan administration's newly announced immigration plan at the Kennedy School Forum, eliciting harsh criticism from a panel of three experts.

Charging that the proposal was weak, unfair, and impractical, Professor Michael Piore of MIT; Julian Soshnick, former chairman of the New England Association of Immigration and Nationality Lawyers; and Rick Swartz, founding member of the National Forum on Immigration and Refugee Policy, agreed that the plan would accomplish very little, and might even escalate rising numbers of illegal aliens.

David Hiller, special assistant to the Attorney General, said the Omnibus Immigration Control Act, which is currently being debated in Congress, would not only make it unlawful for employers knowingly to hire illegal aliens, but would also "substantially beef up the Immigration Service with desperately needed money and manpower."

He added that the proposal gives "permanent alien resident status" to immigrants meeting certain requirements, and also sets down guidelines for a two-year experimental "guest worker" program.

Soshnick, calling the Reagan plan "asinine" said he felt the program was weak and misdirected. He added he saw no good reason to allow "uneducated, unsophisticated aliens" who have "nothing to add except broad backs" into our country.

"Word is out that we're patsies--get your foot in our door and we'll never throw you out," he said, adding, "What we've got to do is bite the bullet. We need a strong national immigration policy--we need to attack the root problems."

The Reagan plan is plagued by loopholes and inadequacies that made it "ludicrous and absurd," Soshnick said.

Attacking the Reagan policy of dealing with aliens as "a giant mass of impoverished humanity washed up on our shores," Piore said there is no such thing as a good or bad immigration program. The problem, he said, lies in the perceptions of the issue, adding, "if we conceived of the refugees as real human beings, we wouldn't pursue this 'push back the tide' Reagan program."

Swartz added that the Reagan plan "just makes no sense," calling the plan an overly simplistic, irrational reaction to American resentment of aliens.