President Reagan's tax reform plan has splintered the business community, which yesterday began the difficult process of calculating the benefits and costs of the major overhaul in corporate taxation that he has proposed.

There was widespread support for the goal of a "level playing field" -- the idea that all companies should be taxed on a fairer, more equal basis than they are currently. But predictably, the companies and industries with the most to lose from the president's proposals quickly raised alarms.

Alexander Trowbridge, president of the National Association of Manufacturers, reflected that divided view. In a statement yesterday, Trowbridge called the president's plan "a major improvement" over the administration's first tax reform plan of last year, dubbed "Treasury 1." But Trowbridge also was worried about the tax advantages that businesses would lose from the president's plan, which raises corporate taxes by 22.5 percent by 1990 in order to achieve a 5.2 percent reduction in individual taxes in that year.

In addition to lowering corporate taxes, the new plan provides a lower rate for small business and a continued preferential treatment for capital gains. It continues, if on a reduced basis, a system of accelerated write-offs for new investments.

Finally, Trowbridge said, the president's plan takes a first step toward eliminating double taxation of dividends. "There is a great deal in this proposal that will encourage small entrepreneurial firms," he said.

"But there are areas of concern," Trowbridge added. "The plan would raise corporate taxes by nearly $120 billion over five years," he said. And Trowbridge worried that the effect of the tax changes could be to raise industry's cost of capital, impairing the ability of U.S. manufacturers to compete in world markets.

Even such a central point as that, however, was in dispute yesterday as economists and corporate treasurers began reviewing the plan.

The clear winners include the high-tech sector, which was singled out by President Reagan in his televised speech Tuesday as the key to the economy's growth.

"Virtually everything that the high-tech sector could have asked for is in there," said Rep. Ed Zschau (R-Calif.), head of a House Republican high-tech caucus.