Lionel H. Olmer is ending his tour as one of the Reagan administration's leading figures on trade issues by accompanying his boss, Commerce Secretary Malcolm Baldrige, on a journey that will take them to Peking, New Delhi and Moscow.

But Olmer isn't through with his traveling. Before he resigns in mid-June as undersecretary for international trade and head of the International Trade Administration, Olmer expects to make yet another trip to Tokyo to put more pressure on the Japanese to open their markets to American high technology.

Waiting to occupy Olmer's hot seat is S. Bruce Smart Jr., who left his job as chairman and chief executive officer of the Continental Group Inc. in February after a merger. Smart's appointment has not yet been made public, although he has been at Commerce for weeks getting to know his new job. Commerce officials say they are waiting for Olmer to submit his resignation officially before announcing Smart's nomination.

Olmer made no secret of his forthcoming departure when he testified this month before the House Banking, Finance and Urban Affairs subcommittee on economic stabilization. The congressmen praised him for efforts to open Japan's markets to U.S. products.

Olmer has not said where he will land after he leaves Commerce, although most informed observers expect that he will join a major law firm here as a trade specialist.

It is unclear how much experience Smart has in international trade, which has become an increasingly important area of the Commerce Department. Last year, Baldrige reorganized the department and gave the International Trade Administration all divisions involved with trade policy.

Except for his membership in the Council on Foreign Relations, Smart appears to have focused primarily on domestic products, sales and planning during his 32 years with the conglomerate Continental Group.

Although Baldrige and Smart share a similar background as Connecticut business executives, Baldrige aides said they hardly knew each other before coming to Washington. They both belong to the Business Council, composed of past and present executives of America's largest and most powerful corporations.

TOKYO TALKS . . . There are reports that some Japanese officials cringed when they learned Olmer was going to make one last official trip to Tokyo to continue talks about opening markets there. The Japanese apparently thought they had gotten rid of him when he declared in early April that talks aimed at opening Japan's formerly government-owned telecommunications industry had been "surprisingly successful."

But then he said those talks had tackled just one-third of the problem of selling more American high technology in Japan. Still to come are such issues as the radio laws that prevent U.S. companies from selling internationally accepted equipment such as pagers and mobile phones; telecommunications equipment to the government, and computers in Japan.

Olmer says he will lay out all the issues "from now till Doomsday" when he goes to Tokyo on June 3 and 4.