Conrad P. Heins Jr., a University of Maryland expert on bridge construction, had finished his lectures in China and was about to land at the Canton airport last week on his way home when fire broke out in his plane.

Heins, an international authority on improving the strength of elevated roadways and bridges, was one of three Americans among the 23 persons killed in the airplane accident on Christmas Eve.

"It's a very tragic, unfortunate thing," said Matthew W. Witczak, chairman of the department of civil engineering at the University of Maryland. "Very few people have realized the heights he achieved in engineering . . . . Particularly at a time when the university is attempting to achieve national excellence and prominence, it's a bitter blow."

The 45-year-old structural engineer had left his home in Laurel Dec. 2 on a 7,000-mile journey that relatives said would be his third or fourth visit to China in the last several years. His first lectures on this trip, according to colleagues, were given at Tongji University in Shanghai, and the last were delivered during a five-day stop in Beijing.

Among the topics addressed by Heins, who was a specialist in applied mathematics, was the effects of earthquakes on bridges and buildings. According to colleagues, the subject was one in which Heins, the author of at least five engineering textbooks and numerous articles, had recently developed an interest.

Witczak and other department heads said Heins traveled frequently to attend and speak at international engineering meetings in locations ranging from the Soviet Union to Japan, Taiwan, Korea and West Germany. He had last been in China in September to serve as U.S. coordinator for the Sino-American symposium on bridge and structural engineering, held at Tongji University.

Heins had also been a consultant in a variety of research projects, ranging from a study of oil platforms for Exxon Corp., to one of the causes of bridge failure for the U.S. Department of Transportation. His work had won him numerous prizes and accolades, both for teaching and research work.

Heins was divorced and had two children. Funeral arrangements are incomplete, a family member said.