In the politics of the bidding war for votes on the tax bill, Democrats and Republicans were constantly calling and raising each other on special interest breaks, with only one major exception -- small business.

In the final months of the bitter partisan fight, Democrats proposed what amounted to a $24.2 billion set of tax breaks designed to win the backing of small and medium-sized businesses, a force of significant leverage in the political process.

In every other instance where the Democrats tried such a move -- $15.5 billion in estate tax breaks or $9.2 billion worth of reductions in the windfall profits tax on oil -- the administration either matched the proposal, as it did for estates, or raised the bid, as in the case of oil to over $16 billion.

On small business, however, the administration was able to depend on the continued loyalty of one key group, the National Federation of Independent Businessmen, and consequently did not have to make as many significant concessions.

"More provisions didn't go in, probably because we didn't remain as uncommitted" as such interests as the Independent Petroleum Association and its oil-state congressional allies, said John Motley, deputy legislative director of the NFIB, in explaining why his group didn't win more for small business.

In the end, the administration bill provided modest reductions in the two lowest corporate income tax bracket; expensing -- or one-year investment write-offs -- for up to $5,000 in 1982 and growing to $10,000 in 1986; and an increase in the credit against accumulated earnings from $150,000 to $250,000.The value of these breaks is just under $6 billion through fiscal year 1986, or about 25 percent of the value of the breaks in the Democratic bill.

Motley argued that the membership of the NFIB is nearly unanimous in its support of the Reagan administration and that the membership found other general provisions of the administration bill -- indexing and the 25 percent across-the-board individual cuts -- so attractive that the lobby could not fully enter into the competitive bidding process demanding additional breaks in return for support.

Others, including officials of a competing but less influential lobby, the National Small Business Association, contend that the NFIB locked itself into the administration bill early in the process and failed to recognize the disproportionate edge given big business in the legislation.

"I don't know why they [the NFIB] got involved at the beginning of this thing," Herbert Liebenson, president of the National Small Business Association said. Liebenson argued that the original group that engineered the $10-5-3" accelerated depreciation bill in the late 1970's was dominated by such "big business" interests as the Chamber of Commerce, the National Association of Manufactures and Charls Walker's American Council for Capital Formation. The NFIB was a partner in this group which produced the 10-5-3 bill, the basic elements of which were subsequently incorporated into the Reagan tax bill as the core of the business tax cuts.

The basic differences on small business provisions between the rejected Democratic bill and the measure as passed are:

Corporate rates. The GOP bill lowers the rates on corporate income below $50,000 by 2 percentage points by 1983. The Democratic bill lowered rates and widened brackets on corporate income up to $200,000, fully effective in 1983. For corporate income below $25,000, the GOP bill is more advantageous. For all other income, the Democratic bill had larger marginal cuts.

Expensing. The GOP bill allows businesses to write off up to $50,000 in personal property in 1982 and 1983, $7,500 in 1984 and $10,000 thereafter. The Democratic bill would have immediately allowed this simplified and accelerated method of one-year write-offs to apply to $25,000 worth of investment starting this year.

Both bills increased the accumulated earnings credit from $150,000 to $250,000 in 1982.