Vietnam, angered by "hostile" U.S. policy, said Wednesday it has suspended plans to search jointly for missing American servicemen and allow former political prisoners to resettle in the United States.

The abrupt changes, sparked by the Reagan administration's steadfast refusal to upgrade diplomatic contact with Hanoi, reversed a recent warming trend in U.S.-Vietnamese ties."Vietnamese Foreign Minister Nguyen Co Thach says Vietnam is compelled to temporarily (stop) the United States from joining Vietnam in the search and exhumation of the remains of (Americans) missing in action as well as the resettlment of released (re-education) camp inmates in the United States," the Voice of Vietnam radio said.

The radio said Thach notified the United States of the halt in a letter dated July 31 to Gen. John Vessey, Reagan's special envoy on the fate of nearly 2,400 Americans still listed as missing in action from the Indochina War.

The broadcast said Thach was reacting to testimony by Assistant Secretary of State Gaston Sigur three days earlier before the House Foreign Affairs committee. Sigur said the Reagan administration opposed a congressional proposal to establish U.S. and Vietnamese interest sections in friendly embassies in Hanoi and Washington.

The establishment of such sections would have meant the first permanent diplomatic contact between the two former war foes.

Sigur said no such improvement should be made until Vietnam ends its 91/2-year-old occupation of neighboring Cambodia.