WASHINGTON (AP) _ Felix S. Bloch's friends describe him as a dry, competent U.S. diplomat who displayed a deep grasp of European affairs befitting his 30 years experience.

Now they are asking if he hid from them a secret of betrayal and intrigue, perhaps dating back more than a decade.

Bloch, 54, a career State Department official, is suspected but not charged with passing secrets to the Soviets, federal officials say. Authorities kept him under tight surveillance Monday in New York.

Friends and colleagues spoke of Bloch as a precise, analytical man respected in his field but seemingly frustrated at the pace of his government career.

''Dry, bureaucratic, competent, ambitious,'' was the description offered by his friend, Austrian Foreign Minister Alois Mock, who has known Bloch and his wife Lucille since the 1950s.

Bloch served in the U.S. Embassy in Vienna from 1980-1987, most of that time holding the No. 2 post in the embassy. There he ''went in and out of the highest Austrian offices,'' Mock said.

A harsher assessment of his time in Vienna was offered by former Ambassador Ronald Lauder.

''I did not like him,'' said Lauder, who is now a Republican candidate for mayor of New York City.

''There was something about him that bothered me,'' Lauder said on ABC's ''Good Morning America'' program. ''The more I got to know him the more I realized there was something dramatically wrong.''

Lauder, however, said he didn't suspect espionage.

He called Bloch ''a very dour man'' and ''a poor staff manager.''

But Bloch appeared to be more highly regarded among others.

A former Austrian official, Ernst Eugen Veselsky, called Bloch ''substantiall y more knowledgeable than others.''

Bloch returned to Washington in 1987 and became director of the State Department's office of European regional political-economic affairs. He was considered a top specialist on the European Community.

In fact, Bloch is the author of an article featured on the cover of the current issue of Foreign Service Journal, the monthly magazine of the American Foreign Service Association, a professional organization of State Department employees. It is a readable discussion of Europe's moves toward economic unification, and U.S. policy toward the changes.

According to news reports, officials say that Bloch was filmed by U.S. officials earlier this year passing a briefcase to a Soviet KGB agent in a European capital. The State Department issued a statement saying it and the FBI were ''pursuing the inquiry thoroughly in order to identify the compromised security which has occurred and the appropriate steps.''

Bloch was born in Austria and left that country at the age of 3 with his Jewish parents. He and his wife met Mock while studying in Italy in 1957-58. Bloch is a graduate of the University of Pennsylvania and holds a master's degree from the University of California at Berkeley.

He held a variety of State Department jobs, including economic counselor at the U.S. Embassy in East Berlin in 1974. He later was an inspector who traveled to various embassies.

In Austria, Bloch was deputy chief of mission, considered a particularly important job when the ambassador is not a career foreign service officer. He served under Reagan appointees Lauder, and before that, Helene Van Damm, a longtime aide to Reagan.

The Washington Post quoted unnamed colleagues as saying Bloch had become frustrated over his failure to obtain an appointment as ambassador. But investigators have indicated their suspicions go beyond recent activities, suggesting they do not consider career advancement to be a motive.

Mock told reporters in Austria that he learned of suspicions about Bloch three weeks ago and that ''there was an allusion this might go back to the 1970s.''