WIMBLEDON, England — The United States Open will test a 25-second countdown clock between points and allow coaching from the stands during its qualifying tournament and several main-draw events this year, part of a package of changes intended to make the sport more appealing to modern audiences.

The moves, confirmed on Thursday by Stacey Allaster, the chief executive for professional tennis at the United States Tennis Association, will not extend to the five main-draw events: men’s and women’s singles and doubles, and mixed doubles.

At least not yet.

“I think it’s one step at a time,” Allaster said in a telephone interview.

The changes, some of which were first reported by The Daily Telegraph, also will be used in the junior, wheelchair and American Collegiate Invitational events at the Open.

Allaster said the moves had been approved after consultation with officials from Wimbledon, the Australian Open and the French Open.