A reader, Dorothy M. Rogers of Boston, suggests the following for a unique place to lunchm : A nice change of pace from commercial New York City restaurants is the experience of dining in the United Nations Delegates Dining Room. It's open to the public on a space-available basis. Reservation procedure is simple: just call in the morning. The room is open from 11:30 a.m. to 2:30 p.m., and normally there are free tables until about 12:45. Men are required to wear neckties and jackets, and women must be presentable - no back-packing garb for anyone. Native robes and head gear are most welcome; they lend a marvelous international ambiance, as do the snatches of conversations from nearby tables, from a ''Mais oui . . .'' to rare dialects from interior Africa.
The room itself is United Nations blue, just bare walls except for one clock. Why not a few pieces of the renowned art that is on exhibit elsewhere? One reason is to avoid the appearance of favoritism. More important, the art that has been contributed is for everyone to enjoy, and not everyone eats in the Delegates Room. White tablecloths complete the UN colors, and fresh flowers on each table add a bit of grace.
A focal point is the large, circular pastry table. The desserts and the entire menu can best be described as international hotel cuisine. The service is attentive, the portions generous, the food reasonable, and the prices, especially by New York City standards, are most moderate. The luncheon is actually a dinner, so visitors may want to plan for just a snack that evening.