The State Department confirmed yesterday that James L. Malone will be replaced as assistant secretary for scientific affairs, but it denied in strong terms a Washington Post report that Malone is being moved because of inability to work out "a politically acceptable policy" for increased foreign sales of U.S. nuclear technology.

The Post article, published yesterday, said Malone was being dropped from the assistant secretary's job but would continue as head of the U.S. delegation to the Law of the Sea Conference, which resumed at the United Nations yesterday.

State Department spokesman Dean Fischer, after calling The Post article "inaccurate in all respects," said Malone would head the Law of the Sea delegation and someone else would be named to the assistant secretary post.

Fischer's statement added that heading the delegation "requires the full and undivided attention of the senior U.S. official" and that Malone had the "full confidence of the secretary of state" in pursuing President Reagan's nuclear policies.

The spokesman also denied that Richard T. Kennedy, undersecretary for management, had assumed "de facto control" of the department's nuclear policy functions. The Post article quoted sources, who asked not to be identified, as saying that was the case.

Fischer's statement also questioned "the normal journalist ethics and sensible practice" of not consulting those mentioned in the article. As the article noted, several attempts were made by a Post reporter to contact Malone. He refused to return the calls and finally referred the reporter to a spokesman who said there would be "no comment" on questions about Malone's status as assistant secretary.