The Trump administration is planning to tell Russian leaders next week that it is preparing to exit the landmark Intermediate-Range Nuclear Forces Treaty, according to American officials and foreign diplomats.

President Trump has been moving toward leaving the three-decade-old treaty because Russia has been violating it for years and because it is constraining the United States from deploying new weapons to counter the growing arsenal of intermediate-range weapons that China has deployed in seeking greater influence in the Western Pacific.

The White House said that no official decision had been made to leave the treaty, known as I.N.F., which was signed in 1987 by Ronald Reagan and was considered a critical step in defusing Cold War tensions. In the coming weeks, Mr. Trump is expected to sign off on the decision, which would mark the first time he has scrapped a major arms control treaty.