Katherine Ozer was the leader of the National Family Farm Coalition, an advocacy group for small farmers. (Family photo)

Katherine Ozer, a longtime advocate for small farmers, farmworkers and sustainable agriculture, who helped lead the push for federal legislation to ease credit for financially strapped farmers, died Jan. 22 at a hospital in Philadelphia. She was 58.

The cause was non-Hodgkin’s lymphoma, said her husband, David Battey.

Ms. Ozer, who lived in Washington, joined the National Family Farm Coalition soon after its founding in 1986 and had been executive director for the past 24 years.

The coalition, which encompasses 25 organizations nationally, works on policy initiatives to support fair prices for small farmers and to protect their land from predatory buyers.

Ms. Ozer helped draft and promote the Agricultural Credit Act of 1987, which was passed by Congress in the wake of a severe economic downturn that drove thousands of farmers off the land. It helped many more beleaguered farmers, threatened with the loss of their livelihoods, to renegotiate terms of their loans.

“Family farmers in this country had no better advocate in D.C. than Kathy Ozer,” said Lorette Picciano, executive director of Rural Coalition, who worked alongside Ms. Ozer on a variety of issues. “She was quite a force who worked behind the scenes with very little credit, but she connected all the groups.”

Ms. Ozer was a liaison to dozens of agriculture-related organizations in the United States and abroad, including Farm Aid, which features celebrity-studded concerts to raise funds for family farmers. She also worked on early efforts to promote sustainable agriculture and country-of-origin labels on food and argued against introducing genetically modified foods to the public.

In the 1990s, Ms. Ozer unsuccessfully lobbied members of Congress to reject the North American Free Trade Agreement, arguing that it would hurt farmers in the United States and Mexico. The issue of NAFTA’s fairness became a major topic in the 2016 presidential campaign.

In recent years, Ms. Ozer fought to gain sustained funding for the Agriculture Department’s Grain Inspection, Packers & Stockyards Administration, which is designed to help small farmers receive fair payment from giant poultry and meat companies.

“She pushed some of the most difficult challenges facing rural America,” Rep. Marcy Kaptur (D-Ohio) said in an interview. “She fought for decades. I’m the longest-serving woman in Congress, and I have met thousands of people. She remains in the top tier of Americans who have made a difference.”

Katherine Ann Ozer was born Aug. 4, 1958, in San Francisco and grew up mostly in Bethesda, Md., on what had once been a farm. Her father is a neurologist.

She was a 1976 graduate of the Sidwell Friends private school in Washington and received a bachelor’s degree in economics in 1980 from the University of Massachusetts at Amherst.

She became an activist in college, participating in environmental campaigns and anti-apartheid rallies. She worked for four years at the United States Student Association before joining the farm coalition.

Survivors include David Battey, her partner of more than 30 years and husband since 1995, of Washington; her mother, Ann Ozer of Palo Alto, Calif.; her father, Mark N. Ozer, and stepmother, Martha Ozer, of Washington; a brother, Mark P. Ozer of New York City; and three sisters, Elizabeth Ozer and Emily Ozer, both of San Francisco, and Nicole Ozer of Oakland, Calif.

Ms. Ozer was a representative at agricultural conferences around the globe and was a past or present board member of such organizations as the Citizens Trade Campaign, Community Food Security Coalition and Environmental Mediation Center.

“Kathy was in the front lines of the battle,” Kaptur said. “She was her own constellation on behalf of the farmers she represented.”