The House of Representatives took a giant step yesterday toward a direct confrontation with the White House over trade legislation when a key subcommittee defied a presidential veto threat and approved a bill giving U.S. textile protection from imports.

President Reagan, reacting to strong pressure from Congress that he do something to end a flood of imports seen as costing the country as many as 3,500 jobs a day, will unveil his own trade program in a speech Monday to a group of businessmen brought into the East Room of the White House.

In his press conference Tuesday and a speech Wednesday, the president warned against "a mindless stampede toward protectionism that will be a one-way trip to economic disaster." He has threated to veto the textile bill and any other protectionist legislation.

Nonethless, legislation to protect American textile manufacturers from import competition is likely to be the first of a string of trade bills to come before a Congress that returned from the August recess determined to improve America's trade posture.

"President Reagan seems willing to preside over the de-industrialization of America. We in the Congress are not," said House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.)

The textile bill was reported out of the Ways and Means Committee's trade subcommittee yesterday over the objections of its chairman, Rep. Sam Gibbon (D-Fla.). Passage was by voice vote in a closed session of the subcommittee.

The bill, with about two-thirds of the House and at least half the Senate as cosponsors, is due to be reported out by the full Ways and Means Committee next Thursday and could reach the House floor as early as the week of Sept. 30. Ways and Means Committee Chairman Dan Rostenkowski, who opposes the bill, has said he wants it to come for a vote in a fashion that would bar amendments setting quotas on imports for other industries such as shoes.

That requires a two-thirds majority of the House -- the same number needed to override a presidential veto -- which Rep. William Frenzel (R-Minn.), a leading opponent, predicted the measure could get by a narrow margin.

As an indication of congressional intent to move speedily on trade legislation, reports circulated on Capitol Hill last night that the Senate version of the textile bill could come up as early as today as an amendment to a Micronesia trade bill.

The Reagan administration appears split on what specific legislation it will support, forcing Senate and House Republicans to draft separate trade initiatives despite presidential assurances last week that his administration would work on a GOP bill, Hill sources said.

"We've had trouble getting clear signals from the White House," a Republican Hill source said. Nonetheless, House Republicans hope to put finishing touches on their plan today and release it next week.

House Democrats, meanwhile, approved their own broad legislative agenda for trade yesterday. It lends support for legislation resembling a bill sponsored by Rostenkowski, Rep. Richard A. Gephardt (D-Mo.) and Sen. Lloyd Bentsen (D-Tex.) that would penalize nations with large trade surpluses who fail to open their markets to U.S. products.

Other points in the Democratic agenda call for bringing down the high dollar, aggressively promoting U.S. exports with low cost financing, strengthing laws against unfair trade practices and barriers to U.S. products and increasing aid to American workers and firms hurt by imports.

The resolution, which was sponsored by Rep. Stan Lundine (D-N.Y.), sets a fast timetable, with committee approval of legislation by Oct. 30 and House passage before the end of the year. House sources said it is unlikely that the Ways and Means Committee, crucial to passage of any trade bill, will be able to keep that schedule.

The textile bill takes a narrower approach, aimed at protecting an industry that says it is badly battered by government subsidized imports that surged 32 percent last year on top of a 25 percent increase in 1983. Its prime sponsors are Rep. Ed Jenkins (D-Ga.) and Sen. Strom Thurmond (R-S.C.).

The measure would drastically cut already established quotas on textile imports from Third World nations, largely in Asia, while leaving untouched shipments from Canada and Western Europe, which also have increased dramatically in recent years.