WASHINGTON (AP) _ Secretary of State George P. Shultz announced today that the United States and Japan have concluded an agreement allowing United Airlines to take over Tokyo landing rights held by Pan American World Airways.

The agreement will allow United to begin operations Feb. 11 on the Pacific routes that it has agreed to purchase from Pan Am for $715 million.

Japan had balked at allowing United to become the designated U.S. carrier for the routes under a bilateral aviation agreement with the United States.

The agreement Shultz announced was signed by Deputy Assistant Secretary of State Jeffrey Shane and Makoto Wantabe, deputy director general of the Japanese Ministry of Foreign Affairs. It was also signed by Tadakuni Hirano, a Ministry of Transport official.

United announced last April that it was buying Pan Am's Pacific division. But the deal had been held up because Japan's reluctance to let United take over Pan Am's Tokyo landing rights.

Japan's approval was needed because many of the Pacific flights land in Tokyo. George Aste, a United vice president, said the company expects to get landing rights in the other Pacific and Far East nations served by Pan Am.

In addition to Japan, Pan Am currently flies to South Korea, the Philippines, Australia, New Zealand, China, Singapore, Taiwan and Thailand.

''This has been an important issue for our two governments, and it received attention at the very highest levels,'' Shane said.

''President Reagan made his personal concern known to Finance Minister (Noboru) Takeshita during a meeting earlier this week,'' Shane said.