The United States has begun denying travel visas to Czechoslovakian citizens in retaliation for the Czech government's detention of naturalized U.S. citizen Vladimir J. Kazan-Komarek, owner of the Harvard Travel Service.

The Czech-born Kazan-Komarek has been held in Prague on charges of treason and espionage since last October 31.

According to a State Department Spokesman, the U.S. hopes the visa veto will help secure his release. The move could cripple Czech hopes for increased U.S. trade by denying visas to Czech trade representatives.

Czech security police seized Kazan-Komarek after a Soviet airplane on which he was returning from Moscow to Paris made what was described as an emergency landing in Prague.

The Czech government charged him with espionage activity for the U.S. at the time of the Communist takeover in 1948. The State Department expects that he will be brought to trial on the charges, but no trial date has yet been set.

U.S. embassy officials visited the imprisoned travel agent on November 23 and December 16, and reported him in good physical condition.

Czech officials have restricted embassy conversations with Kazan-Komarek to matters of health and personal wishes.