An article yesterday incorrectly reported that the National Association of Manufacturers has no official position on tax simplification. It favors tax simplification in principle, but has no official position on the Treasury Department's proposal.

In mid-January, the National Association of Manufacturers issued a report warning that the Treasury Department's tax-simplification plan would harm capital formation and productivity, and could have a "highly unfavorable" effect on economic growth.

One week later at the regular NAM board of directors meeting, executives of such companies as General Motors and Procter & Gamble protested, saying they did not want their association criticizing a proposal that would lower tax rates for their firms. A flurry of letters from other members made the same point.

Today, the NAM has no official position on tax simplification.

When NAM Chairman Stanley C. Pace of TRW met with Treasury Secretary James A. Baker III on Friday, he endorsed the concept of reform and lower rates, but expressed concern about some of the investment provisions. "We are not going to pick sides," said NAM Vice President Jerry Jasinowski.

As the NAM's experience shows, the lobbying battle lines on tax simplification are far from firm. More than three months after the Treasury Department made its proposal and less than two months before the final version is expected to go to Congress, many business interests don't know which side they are on.

"They don't know what their priorities are," said a staff member of the House Ways and Means Committee. "In 1981 [when Congress passed a major business tax cut], it was a monolith."

What initially had appeared to be the largest lobbying extravaganza in recent history is, so far, something of a bust.

Interest groups are making inquiries and retaining some free-lance lobbyists from large Washington firms. Treasury officials meet daily with representatives of industries that would be affected by their plan. But the lobbying effort has not reached a frenzy level.

"I know it's going to mean a lot of business for us in the end, but there hasn't been a huge rush so far," said Niels Hoch, vice president of Gray and Company, a lobbying firm. "A lot of companies are finding that when you run the numbers [on the tax plan] they come out okay."

John M. Albertine, president of the American Business Conference, said there are some problems with the Treasury plan. "But I detect a growing sentiment for the concept," he said. Eighty representatives of the conference's high-growth company members are to meet with President Reagan Wednesday, and Albertine predicted that at least some of them will tell the president they like the plan.

Albertine's perception, however, probably is more accurate for his membership than for the business sector as a whole. Although such umbrella groups as the Chamber of Commerce, NAM and the Business Roundtable find their members divided on tax restructuring, plenty of lobby groups for individual industries have no doubt where they stand.

Industries such as oil and gas, real estate and insurance have begun major campaigns to persuade Treasury and Congress not to do away with their pet provisions. Generally, they plan to use direct-mail and grass-roots lobbying more than in the past, but strategies vary.

The National Association of Realtors, for example, is studying the tax code to see what provisions it can best afford to give up if it has to compromise. Independent oil and gas producers, who have met at least once with Reagan, are hoping to persuade Treasury to ease its curtailment of their tax breaks before the new proposal goes to Capitol Hill.

Insurance associations have hired the same direct-mail company that helped bury Congress in letters protesting withholding of taxes on interest and dividend income.

Nonbusiness groups also are gearing up for the debate. Charitable organizations report that they have generated thousands of local news stories and telephone calls to congressional offices protesting proposed limits on the deductibility of contributions. Organized labor will use its nationwide political network and letter-writing efforts to persuade Congress not to tax employes' fringe benefits.

Compared with all that, some members of the Fortune 500 are far less emphatic. Eleven corporate executives endorsed the notion of simplification at a news conference with congressional sponsors of tax revision.

And Thursday, chief executives of 10 companies, including GM, P&G, International Business Machines, Dart & Kraft, 3M, J.C. Penney and Standard Oil of Ohio, signed a letter to Baker praising the Treasury plan. The letter endorsed cutting tax rates and acknowledged that simplification necessitated "reducing or modifying a number of special-interest deductions, exclusions and credits."

Those sentiments could pale as soon as simplification begins moving through the legislative process. Executives who support doing away with deductions may not have their own in mind. The list of provisions business wants to preserve is long, ranging from accelerated depreciation and the investment tax credit to the capital gains differential and tax-exempt bonds.

"Everybody likes some parts and not others," said former representative James C. Corman, now a tax lawyer and lobbyist. "My incentives are great. Your loopholes are atrocious."