U.S. Steel Corp. Chairman David M. Roderick strongly supported President Reagan's proposed tax policy for business yesterday, while parrying some sharp congressional jabs at the president's controversial tax-cut proposals for individuals.

Roderick, the first business leader to testify before Congress on the president's program, appeared to avoid a full endorsement of Reagan's plan to cut individual rates by 30 percent over three years. Instead, he urged the House Budget Committee and the rest of Congress to take fast action on the entire package of spending and tax reductions.

Would Roderick permit his company to make decisions based on the disputed economic assumptions that underlie the administration's plans? asked committee member Rep. Jim Mattox (D-Tex.), ridiculing the Reagan forecasts as "fantasy" and "dream world" estimates.

"I wouldn't want to answer your question 'yes', obviously, and I wouldn't want to answer it 'no', Roderick replied, ducking the thrust.

"We know what we've been doing [in past administrations] is pretty bad," Roderick continued. "You can't duck that. We have to turn in another direction," he said. And the Reagan proposal does try to point the economy in a different direction, toward greater investment and cutbacks in federal spending, he added.

No one knows what the outcome will be, Roderick said. "I think the direction of what he's trying to do is to be commended."

"Whether 10 percent [per year] is the correct percentage or whether cuts should be prescheduled at that rate for three years will undoubtedly be subject to much debate, but again I feel that we must look at the president's program as a total package," he said at another point.

I agree with the president [that] it is imperative to move on the tax program now," Roderick said.

There was no holding back, however, in his support for the administration's proposed changes in the timing of tax write-off policies for business investment. Roderick said the company's directors Tuesday approved a capital budget calling for $1.2 billion in investments in 1981, a large increase over the $975 million figure for 1980, based in part on the assumption that a business tax program like the administration's will pass.

The average age of steel facilities in the United States is 17 years compared with 11 years in Japan, Roderick said, and it is primarily that difference in the age of steel-making plants and equipment that accounts for any edge that Japan has in steel competition, he added.

U.S. Steel currently can deduct the cost of new equipment from its taxes over an 11-year period, he said. The Reagan proposal would shrink the time period to four or five years, concentrating the tax deduction in half as many years and thus doubling the value of the depreciation tax savings from $500 million to $1 billion, he said. That means a corresponding increase in the after-tax cash available for investment, he said.

In this testimony, Roderick touched on a number of steel industry issues:

Environment. Roderick said the industry is hoping for quick passage of legislation giving steel companies up to three more years to meet air pollution control limits under an agreement reached last fall among the companies, the United Steelworkers Union and the Carter administration.

Black Lung benefits. Roderick said that many retired coal miners now receiving black lung benefits aren't actually suffering from the illness because of a change in the federal black lung disability program. With Social Security, pension benefits and the black lung disability payments, a coal worker who retires after 30 years receives 58 percent more than his working wage, Roderick said. That's "ridiculous" unless a worker is actually disabled with black lung disease, he said.

(Separately, Labor Secretary Raymond J. Donovan told the House Ways and Means Committee yesterday that the administration will propose changes in the black lung program to "eliminate unjustified claims.")

Labor relations. Roderick had kind words for steelworkers, defending their productivity, and he disputed the contentions of several Budget Committee members that high pay scales had badly hurt the U.S. industry's competitiveness.