Harry N. Walters, head of the Veterans Administration for the last three years, plans to resign this month, government sources said yesterday.

Walters, a former assistant secretary of the Army, told a reporter it would be inappropriate for him to comment, but added: "For the last six months to a year it's been no secret that I intended to step down as administrator of the VA. I'm looking to leave government."

The leading candidate to replace Walters, sources said, is Selective Service Director Thomas K. Turnage.

Walters has drawn high marks from veterans' organizations. He has had to walk a tightrope between advocating aid for the nation's 30 million veterans and presiding over a mammoth agency whose $27 billion budget has become conspicuous to budget cutters.

Asked why he took his job, he once said that the best answer came from the late Omar Bradley, the famed five-star general who once headed the VA. Bradley said, "I don't think there is any job in the country that I'd sooner not have and any job in the world that I'd like to do better."

Walters was the first VA administrator who did not serve in the military during a war. He left the Army in 1963 after fulfilling his minimum military obligation in exchange for a West Point education.