Peter H. Silberman, 60, deputy managing editor of The Washington Post, will retire Sept. 7 and his title will be assumed by Robert G. Kaiser, 47, currently assistant managing editor for national news.

The announcements were made yesterday by Benjamin C. Bradlee, executive editor, and Leonard Downie Jr., managing editor of the newspaper.

"Pete has played a big role in the newspaper's drive for excellence during his three decades in the newsroom," Bradlee and Downie said in a written statement that noted the variety of responsibilities Silberman has discharged and praised his "reassuring presence and steady guidance."

At several times over the years, Silberman directed the national news staff, most recently as assistant managing editor from 1981 to 1984. Previously, as an assistant managing editor for financial news, he began the expansion of that staff and launched the Washington Business section.

In his new role, Kaiser will assist the managing editor in day-to-day handling of news, and will have special responsibility for the newspaper's weekend editions and for its weekly sections.

The Outlook, Book World, Health, Home, Food, Travel and TV Week sections, as well as polling and recruiting, will be under his authority.

During his 27-year career at The Post, which began with a summer internship, Kaiser covered the District Building and Congress, and served as a foreign correspondent in Vietnam and the Soviet Union. He also has edited Outlook.

The editors' statement indicated that Silberman's responsibilities would be divided among Kaiser and two others.

Polly Povejsil is to become assistant managing editor for administration, planning and special projects. The News Research Center and the newsroom administrative staff will report to her. She will continue to be involved in special newsroom projects.

Assistant Managing Editor Tom Wilkinson will continue as assistant to the managing editor with special responsibility for compensation and career development. Systems, which handles the newsroom's computers, also will report to him.

Silberman is expected to serve as a consultant on some administrative matters and special projects to facilitate the transition.