SOME OF THE House Democrats are evidently toying with the idea of buying Gulf state votes for their tax bill with a few well-chosen oil tax exemptions. If they go very far down the road, their version of the bill will be no better, by any standard of social equity, than President Reagan's. In regard to its complexity -- owning to its rapidly growing hodgepodge of special breaks, tips and concessions -- it would be a great deal worse.

The independent oil producers have been lobbying assiduously for an exemption to the windfall tax. When you hear the pleas to exempt the producer's first little 1,000 barrels a day, keep it in mind that his little 1,000 barrels a day are worth something over $12 million a year.

The windfall tax was imposed by Congress to retrieve, for the public, a small part of the enormous flow of wealth to producers that resulted from lifting the price controls on oil. President Carter was altogether right to end the controls. But the flow of wealth turned out to be far greater than anyone imagined in April 1979, when Mr. Carter announced his decision. Because of that Year's oil crisis, the price of oil subsequently doubled, and the windfall tax has turned out to be at best a modest restraint on the enormous diversion of income to the oil industry.

To exempt the independents from it now is utterly without justification. The only purpose is mere vote-catching. The independents are very practiced at putting pressure on their local congressman, and the Democratic leadership does not want to lose its tax cill as it lost its budget bill. Of the 29 renegade Democrats who voted with President Reagan on the budget last month, 23 come from the Gulf states, 13 of them from Texas and Louisiana alone.

Regarding the basic structure of its income tax rates, the Democrats' tax bill is substantially better than Mr. Reagan's. It pushes more of the tax reduction into the lower and middle brackets -- although, you have to concede, the differences are not enormous. Both bills do very well by wealth. The Democrats have accepted the view that big cuts are necessary at the top of the scale, to encourage investment.

The Democrats have also, unfortunately, succumbed to old habits and added a lot of expensive junk to their bill. There are excessively large exemptions for people working abroad. There are new breaks for small corporations and large benefits for various "distressed" industries. There's the notorious savings-and-loan bail-out. If the Ways and Means Committee now begins to add oil tax exemptions, any merit of the bill's basic framework will vanish from sight. It will be totally hidden by the gross and unmanageable load of special preferences and exceptions piled recklessly onto it.