WASHINGTON -- Robert Joseph, the State Department's senior arms control and security official, has resigned.

Joseph submitted his resignation to President Bush amid uncertainty about the future of negotiations to curb nuclear programs in Iran and North Korea. Talks on both fronts have moved slowly, with U.N. penalties against both countries showing limited results. The talks are in recess.

Still, in an interview Thursday, Joseph said, "I think we have a very good record."

He cited Libya's renunciation of weapons of mass destruction and the dissolution of a network headed by A.Q. Khan, a Pakistani scientist who leaked weapons technology to North Korea, Iran and Libya.

Joseph also concentrated on what is now a grouping of more than 80 countries committed to intercepting and inspecting weapons cargo at sea and an initiative to combat nuclear terrorism.

Joseph, who will leave next month, acknowledged trying to stop Iran and North Korea from building nuclear weapons was very hard and he said they posed serious challenges to U.S. security.

While he was not a participant in negotiations with Iran and North Korea, Joseph worked on backup measures, including a financial squeeze on the two governments and putting in place the U.N. penalties.

His departure follows that of several other top diplomatic officials, including Philip Zelikow, a close adviser to Secretary of State Condoleezza Rice; Deputy Secretary Robert Zoellick; and John Bolton, the U.S. ambassador to the United Nations.

Joseph joined the department in 2005 after working on Bush's national security council staff.

He has taken a strong view on a need to eliminate North Korean and Iranian nuclear programs. He warned last month against terrorist groups and other nations acting against U.S. and commercial satellites.

In a telephone interview, he said he would write, teach and work as a consultant. He has compiled 26 years of government service, teaching intermittently over that span.

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