Defense Secretary Caspar W. Weinberger landed here today on his way to the Persian Gulf for discussions with Arab leaders on how to keep that oil region secure.

The Soviet presence in South Yemen, Iran and President Reagan's next steps to continue the Camp David peace process are among the items high on the agenda, according to officials traveling with him.

Weinberger will stay overnight in Britain, attending a private conference on telecommunications at Ditchley Park, a country estate near here.

He leaves Saturday for Riyadh, Saudi Arabia. A defense official on Weinberger's plane said he is expected to complete details on the previously approved purchase of AWACS (airborne warning and control system) planes and F15 fighter jets.

Specialists on Saudi Arabia have noted that the Riyadh government sees Weinberger as the U.S. official closest to President Reagan and likely will seek through the defense secretary a number of assurances, including that Washington will keep pressure on Israel to take further steps toward a Middle East peace agreement.

Weinberger was in Saudi Arabia seven times previously as an executive of the Bechtel Corp. of San Francisco, which participated in many of the giant construction projects in that country.

From Saudi Arabia, Weinberger flies to Muscat, Oman, on the Persian Gulf, for talks on refining existing military arrangements to combat Soviet and Iranian threats to the region.

After a quick visit to a U.S. aircraft carrier in the Arabian Sea, Weinberger is scheduled to fly to Jordan for anticipated discussions on improved air defense weapons, specifically mobile missiles. He also expects to get the Jordanian perspective on the Iranian-Iraqi war. Jordan's King Hussein has been a strong supporter of Iraq.

A high Jordanian official told reporters accompanying Weinberger that Jordan considers Iranian Ayatollah Ruhollah Khomeini such a threat to the Persian Gulf and Middle East that it would serve U.S. interests to sell military equipment to Iraq.

A high defense official on the Weinberger plane--who declined to be identified--said, however, that the Reagan administration has no intention to get involved in the Iranian-Iraqi war.