By JACKIE CALMES

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.

The administration plan to revamp a corporate code that is widely derided as inefficient and anticompetitive has been in the works at Treasury for two years, and is a priority of Mr. Geithner. Yet he has been preoccupied with crisis management, and is unlikely to see the project through since he plans to leave office after this year.

The proposed overhaul “will help level the playing field for businesses and allow the government to collect needed revenue while promoting economic growth,” Mr. Geithner told a Congressional committee last week, without details.

Republicans and business groups complain that the 35 percent corporate tax rate is among the highest in the world, leaving American companies at a competitive disadvantage. They typically seek a 25 percent rate, with many of them saying that the current tax breaks should be kept in place as well.

Nonpartisan tax analysts consistently find that corporations here on average pay just slightly more than their competitors in other developed countries after exploiting the many tax breaks and loopholes. Recent news accounts have highlighted the low effective rates paid by companies like Google, Boeing and General Electric.

One analysis concluded that 115 of the 500 companies in the Standard and Poor’s stock index paid a total corporate tax rate — federal and otherwise — of less than 20 percent over a five-year period. A study by the Government Accountability Office in 2008 found that 55 percent of American companies paid no federal income taxes during at least one year in a seven-year period it studied.

“Under the current tax system, the United States will soon have the highest statutory corporate tax rate among developed countries, within a system that features a large number of tax expenditures for special interests,” said a senior administration official, who did not want to speak ahead of Mr. Geithner except on condition of anonymity.

“This puts American businesses — especially those in areas like manufacturing that are subject to more intense international competition — at a disadvantage. And this system is also unnecessarily complicated for America’s small businesses.”

Earlier this year, Mr. Obama proposed to end tax breaks for companies that move jobs overseas and to create new breaks for those that bring jobs back.

Corporate taxes make up an increasingly small share of the federal government’s revenue, in part because of tax-avoidance maneuvers by businesses.

Mr. Obama is proposing that the simplification of the corporate code should not add to the deficit, and that most or all revenue raised by closing tax breaks should be used to lower rates or offset the cost of new or existing tax breaks favoring manufacturing, clean energy, and research and development activities, according to administration officials.

Mr. Obama is not proposing to overhaul the tax code for individuals, though he has spoken of it as a goal. Both codes were last revamped a quarter-century ago and the accretion of tax breaks in recent years has given rise to widespread calls, including from Mr. Obama’s 2010 Bowles-Simpson fiscal commission, to overhaul the tax systems in a way that raises enough revenue to both lower rates and reduce annual budget deficits.

ut every tax break has its defenders, from homeowners who want their mortgage-interest deduction to corporations protective of depreciation tax breaks.

In October, Dave Camp of Michigan, the chairman of the House Ways and Means Committee, proposed a 25 percent corporate rate without saying how he would offset the sizable revenue loss.

An analysis in November from Congress’s nonpartisan Joint Committee on Taxation, which was requested by House Democrats, reported that even if every corporate tax break were scrapped, the 35 percent corporate rate could not be reduced below 28 percent without adding to deficits. Republicans disputed that, citing a group of relatively obscure tax breaks that the Congressional analysts did not count.

Even so, the administration and Congress would have a political and mathematical challenge in eliminating or reducing tax breaks enough to lower corporate rates as they propose to do without adding to deficits. Underscoring the difficulty, just two popular tax breaks — for accelerated depreciation of businesses’ capital investments and write-offs of research and experimentation costs — account for the bulk of the revenue the government foregoes to benefit corporations.

Not only are those two provisions unlikely to be repealed; the Obama administration and both parties in Congress also support making a separate research credit permanent.

While Mr. Obama has emphasized federal policies to help manufacturers since he took office at the height of the recession — most prominently by rescuing the auto industry — his attention has become even more pronounced as he seeks re-election in battleground states like those in the Midwest where manufacturing is a mainstay.

For tax purposes, however, the administration would have a challenge in defining manufacturing to determine what companies would benefit from a lower rate.

While details were sketchy, an official said Mr. Obama’s tax framework would “refocus the manufacturing deduction and use the savings to reduce the effective rate on manufacturing to no more than 25 percent, while encouraging greater research and development and the production of clean energy.”

For multinational corporations, officials say the administration will oppose any shift to a territorial system of taxing offshore profits, which could exempt most of corporations’ foreign earnings from American income taxes. Mr. Camp and many other Republicans and corporations favor such a change, and are certain to oppose Mr. Obama’s proposal for a minimum tax on foreign earnings.

While the United States is virtually alone in taxing multinational companies’ foreign earnings, it allows the companies to avoid taxes indefinitely by keeping profits overseas. But that encourages accounting schemes and offshore investments, critics say.