Congress couldn't resist.

Tucked away in the $749 billion tax cut bill, the one that President Reagan says will receive the U.S. economy, are some lesser provisions of a more down-home variety.

There is, for example, a special depreciation provision for racehorse owners, courtesy of Sen. Walter D. Huddleston, thoroughbred Kentucky Democrat. Racehorses, Congress has decided in its wisdom, can be written off in three years.

There is a special tax cut for congressional campaign committees; some minor tax forgiveness for New England fishing boat captains, and a tax deduction for state legislators.

But there are other special-interest provisions not in the final bill. Knocked out of it in conference was an offering by Sen. Howell Heflin (-Ala.) to give a special tax credit of $10 a tree for replacement of pecan trees destroyed by Hurricane Frederick in September, 1979.

Also killed: one by Sen. James Sasser (D-Tenn.) for the guys at the gun clubs who handload their own cartridges.

These lesser winners and losers were not the big boys of the tax battle, although, like the oil companies and commodity traders, they too had their pinstriped lobbyists. Likely losses to the Treasury from the so-called "miscellaneous" provisions of this tax bill are not large, a few million here or there. They are like party favors.

But they add flavor to the tax bill.

Take the racehorse provision. In general, this Reagan-influenced bill moved to liberalize depreciation rules. As part of that process, the Treasury Department proposed letting racehorses be written off in five years.

But horse owners, represented by the American Horse Council and several law firms here, quickly pointed out that this would cost rather then save them money, since they now generally write off their horses over only four years. Then Huddleston introduced an amendment providing for a three-year period, at a cost to the Treasury of $19 million in 1981, rising to $121 million in 1984, by one estimate.

Sen. Howard M. Metzenbaum (D-Ohio), self-appointed tax bill policeman, objected, as did Sen. Harry F. Byrd, the economy-minded Virginia independent. A compromise passed the Senate to leave the useful tax life of a racehorse at four years.

Curiously, however, when the tax bill emerged from the all-night House-Senate conference, the final racehorse provision was more or less back to Huddleston's three-year rule. One for the oat-burners.

The pecan powers weren't so lucky. Heflin's provision would have given Alabama pecan famers a double deduction (since they could also write off the original cost of the damaged trees), by it perished in conference.

Sasser's amendment to exempt custom gunsmiths who make 50 or fewer weapons a year from excise taxes, and to give gun clubs and individuals who load their own cartridges a tax break was backed by the National Rifle Association, a Sasser aide said, but "somehow it got lost in the conference."

The tax break for fishing boat owners emerged from a meeting between Sen. William Cohen (R-Maine) and about 40 fishermen in Jonesport, Me., last year. Under present law, boat owners don't have to pay Social Security taxes or withhold income taxes for most of their crews. The Cohen provision, as modified in conference, would also exempt them from federal unemployment taxes for a year.

State legislators, who will be redrawing congressional districts this year, got a break too. They can avoid taxes on the per diem expense allowance they get while state legislatures are in session.

Kentucky Sen. Wendell H. Ford, chairman of the Senate Democratic Campaign Committee, won an easy goody for members of Congress. The invested committees will be taxed at the graduated corporate income tax rates, ranging upward from 15 to 46 percent, rather than all at the maximum 46 percent.

Closely-held corporations were able to kill a requirement in present law that Employe Stock Option Plans (ESOPs) let individual employees vote their stock on corporate policy. Under an amendment by Sen. Ted Stevens (R-Alaska), ESOP boards, more often than not controlled by management, will vote the stock. "It's a defeat for corporate democracy," said Peter H. Harris,an aide to Metzenbaum, who forced a record vote on the issue.