Sander Vanocur, for the past two years chief television critic and syndicated columnist for The Washington Post, will leave the paper and return to broadcasting as an ABC News vice president.

Tom Shales will assume the role of chief TV critic for The Post. Shales, 32, joined the Style section in 1971 and has specialized in TV criticism and reporting. John Carmody will continue as author of The TV Column, a daily feature in Style. Lawrence Laurent remains as editor of the Sunday magazine TV Channels.

Vanocur, 49, will be in charge of special reporting units and a newly formed investigative journalism unit for the network, according to the announcement yesterday by Roone Arledge, the ABC sports president who also took over the network news division on June 1.

An ABC spokesman said Vanocur, an NBC correspondent from 1957 through 1971, will be in charge of all political reporting for the network, including convention and election coverage, and will appear on "various" ABC News programs "from time to time."

Arledge said Vanocur will be based in Washington and responsible for recruiting "the brightest, most talented, uncompromising, hard-nosed reporters available anywhere in the world. His experience and talents in both electronic and print journalism and now as a news executive will be brought to bear in every area of ABC News."

The hiring of Vanocur is seen in industry circles as the first of several appointments to be announced by Arledge as he seeks to revitalize the network's traditionally third-place news operation. But the network would not speculate about future acquisitions yesterday.

While at NBC, Vanocur served as White House correspondent and as national political correspondent. He also anchored NBC's "First Tuesday," an early network "magazine" news show.

Later, he served as senior correspondent for the National Public Affairs Center for Television (NPACT), then the news division of public TV. He left NPACT after a 16-month tenure on Dec. 31, 1972.

Vanocur will assume his ABC duties in late July, according to the network. He joined the Style section on July 7, 1975.

"These past two years at The Washington Post have been among the most satisfying of all my years as a reporter," Vanocur said yesterday.