''I was a very strong opponent of the Vietnam War,'' he said, ''but I also recognized that the people who went to fight were great Americans. I always thought they got a bad shake in life and never got their just recognition.''

Last night these veterans basked in that new-found recognition. ''We answered the call of our country, and when we came back home we were kicked back into society almost like criminals,'' said Bob Moore of West Volusia, Fla., a member of the Air Force security police in Vietnam from 1967 to 1969. ''A phenomenal change has happened over the last few years. You got a whole bunch of people here coming out of the closet, so to speak.''

''To see a city take it upon itself to do this!'' said Mike Milne of Wilkes-Barre, Pa., who has been confined to a wheelchair since his Army tour in Vietnam and Cambodia. ''And in downtown Manhattan. It's unreal. They really pulled a coup.''

Mr. Milne rose partway from his chair to embrace the Mayor, who was later asked what he had told the disabled veteran. ''I said, 'Thank you,' '' Mr. Koch said. ''It's as simple as that.'' Readings From Letters The dedication ceremony included readings from letters by three actors who had served in Vietnam: Anthony Chisholm and Brian Delate, both of whom are appearing in ''Tracers'' at the Public Theater, and Robert Woods, from the ABC-TV daytime drama ''One Life to Live.''

Mr. Trump read a telegram from President Reagan, pledging that the Government would seek ''the fullest possible accounting of your missing comrades in arms.''

Mayor Koch then urged the city to prolong the spirit of the ''Dear America'' celebration - named for a recently published collection of the veterans' letters - long after the blizzard of ticker tape is swept away.

Finally, the Mayor flipped the switch to illuminate the memorial, its fluorescent lights flickering and then settling into a soft yellow glow. That private lighting ceremony was followed by a more public one, a fireworks extravaganza over the East River designed by the Grucci family.