The first major legal battle over the nation's most widely used intrauterine device opened today with attorneys for 17 women arguing that G.D. Searle & Co., the manufacturer, failed to test the IUD adequately and disclose its potential hazards, including ectopic pregnancies and sterility.

Searle overstated the device's safety to physicians and the U.S. Food and Drug Administration, the lawyers said. Their clients traveled to U.S. District Court from around the country to consolidate their individual lawsuits challenging the safety of the Copper 7 device.

The Copper 7, which has been on the market since 1974, is the largest-selling IUD in the country, according to Searle. A spokesman for the company said about 1 million of the devices are in use in the United States.

In their arguments, attorneys for Searle said the Copper 7 was adequately tested and that health problems cited by Copper 7 users are often the result of sexually transmitted diseases rather than the device.

Roger Pardieck, lawyer for the plaintiffs, told the jury of nine men and three women that Searle's clinical trials of the Copper 7 were "fatally flawed" because 31 percent of the 16,000 women in the test sample did not return to their gynecologists for follow-up visits.

The plaintiffs, most of whom appeared to be in their thirties, filled two rows of Judge Joseph H. Young's courtroom today. Several of the women have had hysterectomies as a result of infections; two have had ectopic pregnancies, a pregnancy in a Fallopian tube that can result in sterility or death.

The first witness in the case was a gynecologist hired by the plaintiffs to review Searle's Copper 7 clinical trials. Dr. Albert Haverkamp of Denver General Hospital said the tests were inadequate because they failed to measure the incidence among Copper 7 users of pelvic inflammatory disease (PID), a condition that can lead to ectopic pregancies and sterility. Haverkamp supported the plaintiffs' contention that Copper 7s cause PID, saying the two are "definitely related."

Haverkamp said the Copper 7 can cause infections and allow bacteria to travel to the ovaries and the Fallopian tubes. He said the Copper 7 IUD is not advisable for women who have not had children because of "the high rate of infection and resultant sterility."

Paul F. Strain, an attorney for Searle, argued that the company's testing of the Copper 7 went far beyond what was required by the FDA in sample size and duration. He said the device continues to have "the overwhelming endorsement of the American medical community."

Attorneys for the plaintiffs have subpoenaed hundreds of thousands of documents from Searle, an Illinois-based division of the Monsanto Co. Published reports have said that some internal memorandums reportedly raised questions about the way the clinical trials were conducted.

Another IUD manufacturer, A.H. Robins Co. of Richmond, took its Dalkon Shield off the market in 1974 and has since filed for bankruptcy in the wake of thousands of lawsuits by women who contended that they were injured by the device.

The Searle case has drawn the interest of Planned Parenthood, which recently issued a statement saying it believed that the dangers of the Copper 7 have been overstated. Planned Parenthood officials said they are concerned that adverse publicity could result in the Copper 7 being taken off the market, dramatically reducing the number of IUDs available.