British Foreign Secretary Lord Carrington leaves here Wednesday for a 10-day trip to Turkey, Pakistan, India, Oman and Saudi Arabia to discuss ways to strengthen defenses against the Soviet Union after its invasion of Afghanistan.

His tour is the first by such a high-ranking Western official to the region since the Soviet invasion. It is also the first important step Britain has taken in response to the invasion, besides strong public support of U.S. actions announced by President Carter.

Prime Minister Margaret Thatcher's Conservative government is considering a cut in Soviet trade and lines of credit and canceling official visits and cultural exchanges.

News services added these developments:

West German Chancellor Helmut Schmidt and Spanish Prime Minister Adolfo Suarez, meeting in Madrid, agreed to a common attitude with the United States on Afghanistan, said West German sources.

In Karachi, Pakistani President Zia ul-Haq made his first public statement since the Soviet intervention in neighboring Afghanistan, appealing for worldwide denunciation of the move.

"If the human community remained a silent spectator, then the small countries . . . will not be able to live on the face of the earth," he said in a statement read to a meeting of the Moslem World League.