Arms Control and Disarmament Agency Director Kenneth L. Adelman, suggesting that the arms control work of the Reagan administration is nearly completed, notified President Reagan yesterday that he intends to resign later this year.

Adelman's announcement came as Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze agreed to hold discussions here Sept. 15-17 on a treaty eliminating medium-range and short-range nuclear missiles and a potential summit meeting this year between Reagan and Soviet leader Mikhail Gorbachev.

Adelman, who has directed the ACDA since 1983 and won a reputation as a hard-liner on many arms control issues, said at a news conference he "wanted to leave at a time when it was clear that things were coming up roses on the first good . . . agreement we've had in 10 to 15 years," meaning the prospective medium-range missile treaty.

But Adelman is also known to believe that no agreement between the two superpowers on strategic arms and space weapons will be concluded during the remaining year and a half of Reagan's term in office, and several officials said yesterday this strongly influenced his decision to leave.

The Soviets "show no sign" of wanting additional strategic arms and space weapons agreements, Adelman said yesterday. "Unless the Soviets dramatically change their attitude . . . we'll be dead in the water" in negotiating such agreements by the end of 1988. An agreement on strategic weapons has been the administration's top arms control priority.

Adelman, 41, informed the White House several months ago of his desire to leave for an unspecified "think tank" job, officials said, but delayed an announcement until the prospects for an agreement had improved enough to blunt any impression that he was abandoning a sinking ship.

Although Moscow and Washington remain strongly divided on whether to include 72 U.S. warheads for West German missiles in a medium-range missile treaty, many U.S. officials interpreted Shevardnadze's willingness to meet Shultz as a sign they are determined to settle the dispute.

"I think the Soviets have indicated they want it to go right," Adelman said of the medium-range missile negotiations that began in 1981. "I think the distance that the Soviets have come over the years . . . shows that they want an agreement" this year.

{Veteran Soviet arms control negotiator Viktor Karpov in a Moscow interview with the Associated Press yesterday attacked the U.S. position on the West German missiles, assailing Washington for becoming "more rigid" as an agreement draws near.}

Although Adelman said he plans to leave in mid-October, he added he "would be happy" to stay on through a U.S.-Soviet summit meeting and treaty-signing ceremony.

"As important as arms control is, it isn't everything," Adelman told The Washington Post last year, emphasizing his belief that arms control should occupy a position in U.S.-Soviet relations equal to such other topics as human rights and regional issues.

After barely surviving a bruising Senate confirmation battle, in which he was alleged to be a proponent more of arms expansion than control, Adelman presided over a sharp increase in the agency's budget and general morale.

Over the years, Adelman sometimes sided with Shultz, often sided with Defense Secretary Caspar W. Weinberger, and sometimes urged the White House to adopt an even more conservative position than the Pentagon favored.

He said yesterday he is most proud of "helping to hold the course" in the face of Soviet resistance to the twin themes of the administration's arms control policy: deep reductions in strategic arms and the total elimination of a class of theater arms.

He added that he is also "happy to have launched" a series of annual reports highlighting alleged Soviet treaty violations. His biggest frustration, he said, was the slow pace of the negotiations, which "can drive you nuts."

A press release said Adelman also "hopes to resume teaching Shakespeare," which he taught part-time at Georgetown University in the late 1970s before joining Jeane J. Kirkpatrick in the U.S. delegation at the United Nations.