American textile and apparel makers yesterday launched a new campaign to increase their protection from foreign competition.

The cornerstone of the campaign is a new bill that would roll back U.S. sales by the 20 largest textile-producing nations to 1 percent above their 1984 levels and restrict their growth to another 1 percent a year. Prime sponsors of the legislation were Sen. Strom Thurmond (R-S.C.) and Rep. Edgar L. Jenkins (D-Ga.).

This would hit hardest at such U.S. Pacific allies as Korea, China, Hong Kong, Taiwan and Japan. Canada and members of the European Community are exempt.

Countries with a lesser impact on the U.S. market, whose sales amount to less than 1.25 percent of all imports, would be given a slightly more generous quota -- 115 percent of 1984 levels, except in the case of import-sensitive products where the quotas would drop to 101 percent. Mexico also would be included in this category. The textile makers said this would allow smaller producers to increase their share of the U.S. market.

The domestic industry said that imports now have captured more than half the U.S. markets as sales of overseas-made products have increased 64 percent since 1980.

The textile and apparel industry's push met with immediate opposition from the Retail Industry Trade Action Coalition which, together with farm groups, import-export associations and shipping services, said added quotas would hurt American consumers.

They called textile and apparel makers part of "one of the most protected industries in the world" and said import restrictions add a "hidden tax" of between $3 billion and $4.5 billion to the price Americans pay for clothing.

Elsewhere on Capitol Hill, administration witnesses tried to pursuade skeptical congressmen that President Reagan's six-month-old program to reduce steel imports will accomplish its aim.

Rep. John D. Dingell (D-Mich.), chairman of the House Energy and Commerce Committee's oversight and investigations subcommittee, said he called the hearing to see if the steel program was "meaningful . . . or merely another pig in a poke. The initial indications are not good."

He cited ballooning steel imports in January, which captured a record 31 percent of the U.S. market, and the entry of new suppliers such as Thailand and Turkey, whose shipments raise questions as to whether they actually make the steel or are being used as a transshipment point by countries facing reduced quotas.

Deputy U.S. Trade Representative Robert E. Lighthizer, who negotiated the plan, yesterday insisted that it will work.

But committee members pounded on Assistant Treasury Secretary John M. Walker Jr. over budget cuts for the Customs Service, which they said will cripple its ability to monitor steel imports and make sure countries don't sneak steel products in over their quota limits.