President Reagan's tax plan has so divided traditional business lobbies that many companies are forming new coalitions to protect their flanks -- in some cases, at considerable expense.

Among the best financed is a group of 17 utilities, telecommunications firms, energy companies and heavy manufacturers that pledged $40,000 each toward a $1 million kitty to lobby on behalf of the investment tax credit, which Reagan's plan would repeal, and other incentives for heavy industry.

If left undisturbed by tax revision, the investment credit would slice $140 billion in five years from the taxes of companies investing in machinery, the Treasury Department says. Along with a proposed new tax on companies that benefited from current depreciation write-offs, it would provide a major chunk of the money with which Reagan plans to pay for lower rates.

"The business community was split, and some of my clients said maybe there should be a group of companies with common interests to protect the major incentives for capital investment in the tax law," said tax lobbyist Charls E. Walker, a former Treasury Department official who organized the coalition.

But the split is so deep and fractious that some companies appear hesitant to pool resources with anyone. It involves not only the investment credit, which subsidizes up to 10 percent of the cost of equipment and machinery, but also myriad credits and deductions that for years have favored certain industries and sectors.

GTE, a telecommunications firm approached by Walker's coalition and sympathetic to it, has not yet decided whether to join. Asked why, a GTE official said the current tax battle is "the classic example of every man for himself. It hits so many people in different ways."

As a result, business groups are too divided to take positions on Reagan's plan. The boards of the Chamber of Commerce, the National Association of Manufacturers and the Business Roundtable endorsed general tax reform, but not the president's plan.

Walker's is not the only coalition that has stepped into the breach. Another group of manufacturers and service firms has formed to promote the "underlying principles of the president's tax reform package," but the group's manifesto says members "may disagree with some specific aspects of the proposal."

The differences between that group, the Tax Reform Action Coalition, and Walker's, the Coalition for Jobs, Growth and International Competitiveness, defy traditional lines between sectors and industries.

General Motors is a founder of TRAC, while Ford Motor Co. is in Walker's group. AT&T, which according to a report used the investment credit to save $372 million in 1984 taxes, is a founding member of Walker's coalition. But IBM, with which AT&T seeks to compete in new markets, is a TRAC leader.

The divisions between members of the same industries were displayed starkly before Congress yesterday. Bethlehem Steel Corp. Chairman Donald H. Trautlein endorsed the outlines of the Reagan plan while, on the other side of the Capitol, Inland Steel Co. Chairman Frank Luerssen attacked it.

"Inland believes the apparent bias of the president's proposals against capital intensive industries is unwarranted and dangerous," Luerssen told the House Ways and Means Committee.

"A thesis has been proposed that the president's proposal would severely impact basic industry. We believe that this may be an overstatement," Trautlein said before the Senate Finance Committee.

Businesses seem to be nearly united, however, against the president's plan to require companies to pay back much of the taxes they have deferred through depreciation in recent years. The "recapture" provision would raise $57 billion over four years, and yesterday, business leaders joined some congressional tax writers in criticizing it as too harsh.

"The recapture provision lacks the basic elements of fairness and should not be adopted," GM Corp. Chairman Roger B. Smith told the Finance Committee, while supporting most of the rest of the plan.

But without the recapture provision, the lower tax rates would result in higher deficits, Treasury officials said