Treasury Secretary James A. Baker III will head to Seoul, South Korea, Friday to attend the annual meeting of the International Monetary Fund and the World Bank. He will take along Deputy Secretary Richard G. Darman; David Mulford, assistant secretary for international affairs; Mulford's deputy, Jim Conrow; Kim Hoggard, deputy assistant secretary for public affairs, and Charles Dallara, executive director of the IMF.

At the meetings, Baker and Darman are expected to discuss the administration's new approach to resolving the Third World's debt crisis, placing less emphasis on austerity and more on programs to improve economic growth. The administration is preparing initiatives to involve the World Bank more in trying to improve the debt situation, along with the IMF.

However, at the meetings, the United States will not be prepared to approve a general capital increase for the World Bank. Instead, it may suggest making more efficient use of its current resources.

On Oct. 8, the day he plans to return to the United States, Baker is scheduled to make a speech, probably on the international debt situation.

The meeting also is likely to involve discussions of the new effort devised by Baker and Darman to push the dollar down, with the help of Britain, France, West Germany and Japan. The effort has been so successful so far that last Monday, the day after Baker announced the new strategy, the dollar made its sharpest decline in 12 years. LISTENING IN . . .

Before Baker leaves for Seoul, he will attend the House Ways and Means Committee's debate on President Reagan's tax-revision proposal, according to Treasury officials.

The plan the Ways and Means Committee is starting with is somewhat different from the administration plan devised by Baker. Among other things, the congressional plan would drop the top corporate tax rate from 46 percent to 35 percent, compared with Reagan's proposed cut to 33 percent. The House plan also includes less generous proposals for depreciation, the schedule under which companies write off investments in plant and equipment. NEW FACE . . .

Don Fullerton will become deputy assistant secretary for tax policy, replacing Charles McLure, one of the chief architects of the original tax-revision plan unveiled by then-Treasury Secretary Donald T. Regan. Fullerton has been an associate professor of economics at the University of Virginia and a visiting scholar at the American Enterprise Institute.