ANDOVER — On his first day on the job, Dr. Howard Koh of Andover watched as President Barack Obama signed a tobacco control bill into law.

The moment was extra special for Koh, who is known locally for his efforts on tobacco control, cancer screening, suicide prevention and AIDS treatment and prevention.

Koh was confirmed June 22 by the U.S. Senate as assistant secretary of health in the Department of Health and Human Services and was sworn in on the same day.

It also was the day Obama signed landmark legislation giving the Food and Drug Administration new power to regulate the manufacturing, marketing and sale of tobacco.

"What a way to start the job. That was just an extraordinary moment," said Koh, 57, during a telephone interview from Washington yesterday. "It was just a thrill to be asked. It's a tremendous honor and privilege. I feel so grateful and so humbled by this appointment."

Koh oversees the country's major health agencies, including the Centers for Disease Control and Prevention, the U.S. Food and Drug Administration and the National Institutes of Health. He also will be the leading health adviser to Kathleen Sebelius, secretary of health and human services.

"We look forward to his expertise and advice when it comes to making America's families healthier and our health system stronger," Sebelius said in a statement.

Koh said there is a lot he hopes to accomplish.

"I believe strongly in the power of prevention and I want to promote prevention for all people in this time of reform."

Koh said he also is in favor of national health care.

"Right now we have 50 million Americans without health care. The president has made health care for all one of his priorities. It is an honor to be part of that national discussion. We need health insurance for all people," he said.

Koh said he never imagined being asked by the president to fill this post.

"I wanted to become a doctor to take care of one patient at a time, but I strongly believe in public health and public service," he said.

In Lawrence, he was involved in the mayor's health task force and was instrumental in setting up the mammography unit at Greater Lawrence Family Health Center at its Haverhill Street site.

"(The center) is a model of what we can do to serve," he said. "They have taken care of so many people in need, people who speak a language other than English, and have delivered individual care with a public health care approach."

Koh said he was inspired to become a doctor by his parents, who immigrated to America from Korea.

"As immigrants, they wanted their children to make a difference in society. I thought becoming a doctor was a great way to help people."

This is not the first time Koh, a doctor for more than 30 years, has been called to Washington.

He was appointed by President Bill Clinton to the National Cancer Advisory Board, where he served from 2000 to 2002.

Koh was the Massachusetts Commissioner of Public Health from 1997 to 2003, overseeing four public hospitals and a staff of more than 3,000 professionals.

Before going to Washington, Koh taught public health practice at the Harvard School of Public Health. He also was the school's associate dean for public health practice and director of the Division of Public Health Practice.

Dr. Koh will commute between Washington and Andover. He and his wife, Dr. Claudia Arrigg-Koh, an ophthalmologist in Lawrence, have three children, Daniel, Katherine and Steven Koh.