Congressional supporters of a textile quota bill decided yesterday to wait until August to try to override President Reagan's veto, hoping a worsening trade picture will give them the needed votes.

They also vowed to use the threat of the override to force the Reagan administration to stiffen its stance in negotiations setting new limits on imports of textiles and apparel. The current multifiber arrangement (MFA) expires July 31.

"If the new MFA is not strengthened to give the U.S. textile and apparel industry equal footing with other nations in the international market, then I'll bring the bill back," said Rep. Ed Jenkins (D-Ga.), prime House sponsor of legislation to limit imports of textiles, shoes and copper.

Rep. Carroll A. Campbell Jr. (R-S.C.) added that a Reagan failure to get strict import limits in the new MFA "will strengthen the chances of an override.

"We're either going to have action to stop imports or we are going to override that veto," he added.

Jenkins acknowledged that he presently lacks the two-thirds majority needed for the veto override.

The House set Aug. 6 for an override vote, and supporters of the measure said its closeness to congressional elections could draw lawmakers to their side. The only Constitutional time limit on overriding a veto is that it be done within the two-year term of a Congress.

Reagan delayed his veto until close to 11 p.m. Tuesday to avoid antagonizing some lawmakers whose support he had sought for a tax overhaul measure. "I was for the tax bill," said Jenkins. "I gave one for the Gipper. But the Gipper didn't give me one back."

While representatives of the textile and shoe industries and their congressional supporters attacked the veto, U.S. retailers and exporting nations applauded Reagan.

The government in Taiwan, the largest supplier of textiles to the United States and one of the three Asian nations that would have been hardest hit by the bill, expressed "hearty respect" to Reagan for his veto. South Korea Minister of Trade and Industry Kum Jin-ho called the Reagan veto "a reaffirmation of America's traditional commitment to free trade. . . . "

Even the European Community, which was not touched by the legislation despite its surging textile sales in this country, applauded the veto as "a courageous decision, which we welcome."

Peter V. Handal, chairman of the American Association of Exporters and Importers, said the veto "will protect millions of American consumers" from higher prices and "avoid costly foreign retaliations" against U.S. exports.

Both Handal and Joseph P. O'Neill, coordinator of the retail Action Trade Coalition, urged the president to resist pressure from the textile industry to insist on tough restrictions in the new MFA. Handal said he expects the interests of consumers, retailers and importers will be considered in formulating the American position.

In his veto message, President Reagan merely instructed U.S. Trade Representative Clayton Yeutter "to most aggressively renegotiate the multifiber arrangement on terms no less favorable than present."

The message also instructed Treasury Secretary James A. Baker III, head of the Cabinet-level Economic Policy Council, to determine if textile and apparel imports exceed quotas set in international agreements as the industry had charged. An earlier draft of the message, circulated on Capitol Hill yesterday before the veto, gave that authority to Commerce Secretary Malcolm Baldrige.