THE TEXTILE BILL seemed, a month ago, certain to sweep through Congress and easily overcome a presidential veto. It's a genuinely bad bill -- fiercely protectionist, written to push imports far below present levels and to keep them there. But at first the idea was immensely popular. More than two thirds of the House and well over half the Senate signed on as cosponsors.

Lately the congressional enthusiasm for it has abated. In the Senate its managers have anxiously substituted a diluted version in an attempt to hold their uneasy supporters. The House Ways and Means Committee reported it only after its supporters staved off, by a margin of one vote, an amendment that would have substantially weakened it. The change in the atmosphere suggests that the meaning of this bill is becoming clearer.

The retail trade industry -- department stores, clothing stores and so forth -- have organized a vigorous campaign against it. True, it would save jobs at least temporarily in the American textile industry. It would also raise the prices of textiles and everything that is made from them. That would hurt sales in the stores. The retailers ask pointedly why jobs and profits should be protected in the textile factories at the cost of jobs and profits in the shopping malls.

The farmers have also begun to take an interest in the bill. China, for example, sells textiles to this country and buys substantial amounts of American grain. The Chinese have declared explicitly that if the United States interferes with their textiles, they will find other sources for their wheat. Some of the senators have been hearing from farmers, and that's why the revised draft of the Senate bill drops China from the list of countries that would bear the chief impact of the textile quotas.

Congress is also beginning to be aware of certain aspects of this bill that are not precisely economic but which ought to make any American uncomfortable. The textile restrictions would apply to Latin America, Africa and especially Asia. But Europe and Canada would not be affected. Rep. Sam Gibbons, the chairman of the House Trade subcommittee, has denounced it as a "white man's bill."

The imports come mostly into the inexpensive end of the market. Curbing them would mean that the price increases mainly hit the kinds of clothes bought by people who don't have a lot of money to spend. That's another kind of discrimination that deserves a little more thought than it's been given.

Despite its manifest defects, the bill will probably be passed in one form or another. President Reagan intends to veto it. The real struggle now is over votes to sustain the veto. That will require a change of some congressional minds but, on closer acquaintance with this bill, a good many minds are evidently changing.