I was truly shocked and disappointed to read that Judge Charles Richey had upheld the State Department's decision to close the Palestine Liberation Organization information office {news story, Dec. 3}.

This move may be seen as a good thing by a few narrow-minded people, but in my view it is quite damaging to the United States on three counts: It almost makes a mockery of the freedom of speech guaranteed everyone legally residing in this country by the Constitution; it is sure to cause irreparable damage to America's already tarnished image as an effective peacemaker in the Middle East; and even worse, the decision to close the PLO office was undoubtedly made not because of any clear-cut evidence of ''terrorist'' acts perpetrated by that office, but rather to serve the purposes of a small group of individuals with an enormous amount of control within our government -- the Israeli lobby, spearheaded by the American-Israel Public Affairs Committee.

I believe closing the PLO office is a grave error that this country will in time sorely regret -- especially when it decides to formulate a Middle East foreign policy with some degree of balance. JOAN TYSENN Arlington

The arguments of The Post {editorial, Dec. 2} and the American Civil Liberties Union that the closing of the PLO information office in Washington violates the First Amendment are, to use the words of Judge Richey, who dismissed the ACLU's lawsuit, "utterly meritless."

We represent Rep. Jack Kemp, Sen. Charles Grassley and other cosponsors of pending legislation that would also close the PLO's United Nations office in New York, and the family of Navy diver Robert Stethem, who was murdered in Beirut by hijackers in 1985. In the brief we filed in the ACLU case, we demonstrated that the First Amendment argument was a red herring. The PLO office was ordered closed not because of what it says or publishes, but for what the PLO represents: an organization that is responsible for terrorist activities and that recently appointed Abu Abbas, who was responsible for the hijacking of the Achille Lauro and the slaying of American Leon Klinghoffer, to its executive committee.

To say that the First Amendment was violated here is equivalent to arguing that the government cannot condemn an unsafe building because its occupant happens to be a publisher. In either case, there are legitimate reasons (in the case of the PLO, foreign policy ones) wholly apart from the activity of the occupants that justify the action taken.

The employees of the PLO office may distribute any literature they want, and Americans can freely receive it. But no U.S. citizen has a constitutional right to act as an agent of a foreign power, especially a terrorist organization. Otherwise, foreign policy could easily be frustrated simply by having U.S. citizens run foreign operations on U.S. soil. We're confident that the courts will see it our way, as at least one has already. PAUL D. KAMENAR Executive Legal Director, Washington Legal Foundation Washington