BEIJING — Facing deepening tensions abroad and anxieties at home, China’s leader, Xi Jinping, delivered an unabashed defense of his policies on Tuesday, using a key anniversary to argue that his recipe of guided growth under strong Communist Party control must not waver.

Mr. Xi made his case to some 3,000 officials and guests gathered in the imposing Great Hall of the People in Beijing to commemorate 40 years since China embarked on far-reaching economic changes after decades of upheaval and malaise under Mao Zedong.

The resonant date had inspired expectations among some analysts and investors that Mr. Xi would give clearer priorities to counter economic headwinds and trade tensions that have flared with the United States. But he offered none, referring only obliquely to the economic and diplomatic challenges confronting China.

Instead, he used the meeting, broadcast live on Chinese television, to stress that only the party’s dominance would allow China to continue its stunning transformation into the decades ahead. The first lesson from 40 years of reform, he said, was the need to maintain party leadership “over all tasks.”