WASHINGTON — President Obama will ask Congress to scrub the corporate tax code of dozens of loopholes and subsidies to reduce the top rate to 28 percent, down from 35 percent, while giving preferences to manufacturers that would set their maximum effective rate at 25 percent, a senior administration official said on Tuesday.

Mr. Obama also would establish a minimum tax on multinational corporations’ foreign earnings, the official said, to discourage “accounting games to shift profits abroad” or actual relocation of production overseas.

With the framework for changes that the Treasury secretary, Timothy F. Geithner, will outline on Wednesday, Mr. Obama will enter an election-year debate with Republicans in Congress and in the presidential race who seek even lower taxes for businesses. But an overhaul of the corporate code is unlikely this year, given that political backdrop and the complexity of an undertaking that would generate a lobbying frenzy as businesses vie to defend old tax breaks or win new ones.

The campaign of Mitt Romney, a Republican candidate for president, signalled that he would outline on Wednesday an expanded version of his own tax proposals, which he said on Tuesday would call for a “flatter, fairer, broader-based tax system” that would do more to encourage economic growth. The various Republican candidates, who are scheduled to debate on Wednesday night, have called for cutting the corporate income tax, differing somewhat in the details.