WASHINGTON — Secretary of State John Kerry signaled for the first time on Tuesday that the United States was prepared to ease economic sanctions on Iran without fully resolving evidence suggesting that Iran’s scientists have been involved in secret work on nuclear weapons.

In his first State Department news conference since breaking his leg last month in a bicycling accident, Mr. Kerry suggested major sanctions might be lifted long before international inspectors get definitive answers to their longstanding questions about Iranian experiments and nuclear design work that appeared aimed at developing a bomb. The sanctions block oil sales and financial transfers.

“We’re not fixated on Iran specifically accounting for what they did at one point in time or another,” said Mr. Kerry, who appeared by video from Boston. Instead, he said: “It’s critical to us to know that going forward, those activities have been stopped, and that we can account for that in a legitimate way. That clearly is one of the requirements in our judgment for what has to be achieved in order to have a legitimate agreement.”

The question of how far to press Iran to formally acknowledge in extensive detail what its nuclear scientists have been working on for more than a decade has been a highly contentious issue in the negotiations. Robert J. Einhorn, who was part of the American delegation to the Iran talks until 2013, wrote recently for the Brookings Institution that the question was “perhaps the most difficult unresolved issue” standing in the way of a nuclear agreement with Iran.