The House of Representatives voted unanimously yesterday to approve a bill to make lower-priced generic drugs more widely available, saving consumers an estimated $1 billion during the next decade.

The bill also provides the manufacturers of brand-name drugs with increased patent and marketing protection, incentives that the pharmaceutical industry has argued are critical to encourage development of new drugs.

The bill, which passed the Senate in a nearly identical version by a voice vote last month, was adopted by the House by a vote of 362 to 0. The result of months of negotiations, it had the support of the brand-name pharmaceutical industry, the generic drug industry, consumer and labor groups, and the administration. President Reagan is expected to sign it.

Provisions of the bill would allow more rapid approval of generic versions of some of the best-selling pharmaceutical products in the country, including the tranquilizer Valium, the pain reliever ibuprofen (a prescription drug known as Motrin that is also available over the counter as Nuprin and Advil), the diuretic Dyazide, and the cardiovascular drug Inderal.

At the same time, it would provide up to five more years of patent protection for new brand-name drugs. Drug manufacturers had fought for patent extension, arguing that the time consumed in getting regulatory approval to market a drug cut into the period that it could be sold with patent protection.

"This bill will do more to contain the cost of health care than anything the Congress has done this year," said Rep. Henry A. Waxman (D-Calif.), the principal author of the legislation. "I think this is the most important consumer bill the Congress has adopted this session."

Differences in the House and Senate versions remain to be worked out, but a Senate Labor and Human Resources Committee spokesman said committee Chairman Sen. Orrin G. Hatch (R-Utah), the bill's chief sponsor in the Senate, hopes to do so quickly. But he added that Hatch had not yet seen all the House amendments.

The bill would increase the availability of generic drugs by making a fast-track method for approval available for generic versions of patented drugs approved since 1962. Generic copies of drugs introduced before 1962 could win FDA approval without complete retesting of the generic copies. Before 1962, the manufacturer had only to show that the generic drug was the same as the pioneer drug to win approval as safe and effective.

The fact that the accelerated procedure was not available for drugs approved since 1962 effectively insulated many best-selling drugs from competition from generics. For instance, Dyazide, the third-largest selling drug in the United States, has been without patent since 1981 without any generic version being available.

The principal difference in the two bills is an amendment by Rep. Butler C. Derrick Jr. (D-S.C.) strengthening provisions of current law that require textile and wool products to be labeled to identify country of origin. The amendment would require that the labels be conspicuously displayed and that information on country of origin be contained in catalogue sales descriptions and other advertisements for textile products. A similar provision has been adopted by the Senate, but not as part of the drug measure.

Otherwise, the bill was little changed from the version that passed the Senate Aug. 10 after negotiations with the representatives of a handful of drug companies that threatened to scuttle the bill. Those negotiations were criticized yesterday as back-door dealing that had tilted the bill in favor of the dissident drug companies -- 11 major drug manufacturers who mounted a campaign during the summer to change or kill the bill.

The 11 firms acted after the industry trade association, the Pharmaceutical Manufacturers Association, had agreed to support the bill. The dissident companies, which account for approximately 50 percent of the industry's research and development, included concerns such as Hoffman-LaRoche Inc., Johnson & Johnson, and American Home Products Corp.

Several amendments to undo some of the changes that ended the challenge from the dissidents were handily defeated. One dealt with how long the FDA would be barred from approving a generic drug under legal challenge for patent infringement. The dissidents had won an agreement to make the period 30 months. The amendment would have limited it to 18 months.

Another amendment, which would have applied the provisions of the bill only to prescription drugs and not to over-the-counter remedies, also failed.

Some of the changes agreed to in the final negotiations over the bill and incorporated in the House and Senate versions include allowing the drug company holding multiple patents on a drug to decide which of its patents would be extended. For most products, manufacturers hold multiple patents, and this allows the company to apply the extension to the patent on the most marketable version.

Another change provides marketing protection for some products that are unpatentable but for which significant research has been done to win approval.

The FDA has estimated that the measure's savings to consumers could be as much as $100 million a year for the next 11 years.