The White House has named another temporary science adviser to the president, and a permanent selection may be announced within a week, spokesman Larry Speakes said yesterday.

President Reagan named astrophysicist Richard G. Johnson, effective last Saturday, as the acting adviser and head of the Office of Science and Technology Policy (OSTP), the adviser's traditional position.

The job has been vacant for six months, with deputy science chief John P. McTague filling in. McTague quit last week to become head of research at Ford Motor Co.

Speakes said yesterday that a tentative selection as permanent science adviser has been made and will be announced soon. He did not elaborate.

This week, scientists at the nation's largest general science meeting, the American Association for the Advancement of Science (AAAS) convention in Philadelphia, openly criticized the White House for leaving the permanent post vacant so long.

Johnson, 58, formerly with Lockheed Missiles and Space Co. in California, has been working for the OSTP since November 1983 as assistant director for space science and technology.

Yesterday's announcements came after prominent scientists and officers of major corporations began pressing for the appointment. They argued that many major science-policy questions are being discussed in government without advice from an independent scientific voice in the White House.

The last lengthy period without a science adviser came in the first five months of the Reagan administration when several prominent scientists turned down the job. It was taken by Los Alamos National Laboratory weapons physicist George A. Keyworth, then 42 and unknown in science-policy circles.

The post's importance had diminished under recent presidents and was abolished under President Richard M. Nixon.

The job was redefined by Reagan and, when Keyworth was appointed in May 1981, the new adviser said he would not be an advocate for science but an adviser with a background in science.

He also acted as a White House spokesman on issues, most notably becoming chief advocate of the Strategic Defense Initiative, the space-based missile-defense program also known as "Star Wars."

Although Keyworth was not known as an advocate for the science community in the White House, he was credited with arguing strongly for, and gaining, increases in science agency budgets during a time when cuts were the rule in government.

He resigned last December to open a consulting firm, just before major cuts to science budgets proposed by the administration and cuts prompted by the Gramm-Rudman-Hollings balanced-budget law.