Dr. Abraham B. Bergman, a pediatrician who was instrumental in passing a federal law to combat sudden infant death syndrome, a once misunderstood loss that caused not just parental heartbreak but guilt and blame, and who put his stamp on other enduring public health laws, died on Nov. 10 in Seattle. He was 91.

The cause of his death, on a family member’s boat, was amyloid heart disease, his son Ben Bergman said.

In the 1960s and early ’70s, Dr. Bergman was president of the National Foundation for Sudden Infant Death, a grass-roots group that supported parents who had lost children to what once was commonly called crib death. Although SIDS, as the syndrome became known, was the leading killer of infants less than a year old, its cause was unknown. Parents often blamed themselves, marriages broke up and, in some cases, authorities investigated for child abuse.

“What we do to those parents is crime,” Dr. Bergman told The New York Times in 1972. “The police investigate, there’s a coroner’s inquest, and often the family doctor abandons the parents.”

Dr. Bergman’s group sought to destigmatize SIDS, support grieving parents and raise money for research. Its efforts led to the Sudden Infant Death Syndrome Act of 1974, which appropriated millions of dollars for research.

Dr. Bergman, who called his decades-long advocacy for improving childhood health “political medicine,” was a passionate witness in hearings on Capitol Hill on a variety of issues. He offered heart-wrenching anecdotes and chastised lawmakers for their inaction. But he also worked behind the scenes as a de facto lobbyist to move bills. Cultivating ties to two influential U.S. senators from Washington State, Warren G. Magnuson and Henry M. Jackson, he was unusually successful as a private citizen who influenced legislation.

“Magnuson really trusted Abe, who had his ear and motivated him to do a lot,” said Eric Redman, a former legislative aide to Mr. Magnuson.

In 1967, Dr. Bergman jolted Mr. Magnuson by taking him to the burn unit of a Seattle children’s hospital and showing him young patients who had been badly injured when their clothes caught fire. Before a Senate subcommittee that Mr. Magnuson led, Dr. Bergman held up a flannel nightgown of the kind that a 2-year-old girl has been wearing when it ignited from a space heater, burning her over 85 percent of her body. “You senators are in a position to save far more lives than physicians,” he said. In response, Congress toughened and broadened the Flammable Fabrics Act to require more flame-resistant clothing.

In 1970, Dr. Bergman proposed to Mr. Magnuson the idea for the National Health Service Corps, a federal program to pay health care providers’ student debt in exchange for a stint of doctoring in poor communities. Dr. Bergman enlisted medical students to lobby key members of Congress in their home districts. He personally went to West Virginia to put pressure on Representative Harley Orrin Staggers, whose district was one of the neediest in the country. President Richard M. Nixon signed the National Health Service Corps into law in December 1970, just 10 months after Dr. Bergman had proposed it.

Working with Mr. Jackson’s office, Dr. Bergman also helped draft the Indian Health Care Improvement Act of 1976, which expanded funding for care to Native Americans, and lobbied for its passage on Capitol Hill.

“Jackson effectively added Abe to his staff for the legislative effort,” Mr. Redman recalled.

Abraham Baer Bergman, known as Abe, was born in Seattle on May 11, 1932, to Fred and Minnie (Hurwitz) Bergman. His father owned a luggage store, and his mother was a homemaker.

He graduated from Reed College in 1954 and received his medical degree from Western Reserve University (now Case Western Reserve University) in Cleveland in 1958. He was a pediatric resident at Boston Children’s Hospital and St. Mary’s Hospital in London, where he lived for a time.

He began his career at Seattle Children’s Hospital, where he was director of outpatient services for 19 years, and then moved to Harborview Medical Center, where he was chief of pediatrics from 1983 to 2005. He continued to serve on the faculty of the University of Washington School of Medicine until 2016.

Dr. Bergman’s marriages to Judy Maslin, Ann (Bigelow) Bergman and Suzanne Fiala ended in divorce..

In addition to his son Ben, Dr. Bergman is survived by seven other children: Anna and Matthew Bergman, Sarah Bergman Lewis, Becca Bull and Pavel, Eugeny and Yulia Fiala, who were adopted from orphanages in Russia. He is also survived by six grandchildren.

When Dr. Bergman began researching crib death, experts had largely discarded its many supposed causes, including suffocation in bedclothes, allergy to cows’ milk and lead poisoning. A theory Dr. Bergman proposed was that infants experienced a spasm of the vocal cords that closed off the airway during sleep.

At a research conference in Seattle in 1969, the term sudden infant death syndrome was first formally proposed as a diagnosis.

In 1973, Dr. Bergman testified before Congress, armed with a report about how law enforcement, coroners and parents in 158 communities responded when a child died suddenly in a crib. There were discrepancies in how health authorities treated parents of different races; only half as many Black parents as white parents were told their baby had died from SIDS. One Alabama coroner, quoted in the report, attributed a SIDS death to suffocation because “Blacks do not know how to care for their children properly.”

During the hearing, he castigated lawmakers for their inaction: “Maybe it’s the heat or maybe it’s the smog. Government officials here in Washington are always busy, busy, busy with big problems.”

The Sudden Infant Death Syndrome Act was passed soon after.

Today, the cause of SIDS is still a medical mystery, but the incidence of deaths has declined sharply since 1990. The reason generally cited is an increase in public awareness of risk factors. The American Academy of Pediatrics recommends that parents put babies to sleep on their backs in their first year and that mothers breastfeed infants, which has been shown to lower the risk of SIDS.

Jerry Grinstein, a former Senate aide who later became the chief executive of Delta Air Lines, recalled in an email that Dr. Bergman first approached Commerce Committee staff members about SIDS in the late 1960s, but that it took a few years to develop legislation and public support.

Committee members and staff “got the job done,” Mr. Grinstein wrote. “But it was Abe’s inspiration and persistence to use legislation supported by compelling stories from fellow professionals, plus hurting parents.”