WASHINGTON--The United States and Soviet Union, despite progress in 9 hours of bargaining, failed to crack all the remaining stubborn details blocking a long-range nuclear arms treaty yesterday and planned to resume talks this morning.
Secretary of State James A. Baker and his Soviet counterpart, Alexander Bessmertnykh, ended yesterday's talks at 11:30 p.m.
The State Department announced that they would meet again at 9:30 a.m. today.
"While it was a long day and much was accomplished, not all the issues have been resolved at this time," spokesman Margaret Tutwiler said in a written statement.
Miss Tutwiler said the two ministers would meet the press tomorrow.
Both men delayed their departures from Washington.
Mr. Bessmertnykh had originally been scheduled to leave at 4 p.m. to return to the Soviet Union; Mr. Baker was to leave late this morning to attend the London summit of seven industrialized democracies.
The talks initially had been planned to last just Thursday and Friday.
Despite a news blackout while the talks were going on, the second extension of talks showed a determination to complete a deal.
But the amount of time required by technical experts to work out the complex details mean that if agreement is not reached today, the hoped-for late-July superpower summit may be derailed yet again.
The ever-closer but still-elusive agreement has been the subject of marathon negotiations among U.S. and Soviet technical and military experts at the State Department, with political guidance from Mr. Baker and Mr. Bessmertnykh.
The unsettled issues, while technical, are nevertheless significant because they bear on the mechanisms for ensuring that neither side can cheat or break out of the treaty's limits quickly in the event of a crisis.
Earlier yesterday, National Security Adviser Brent Scowcroft had said the talks were advancing.
"We're making progress on all of the major issues that are outstanding, and while we've not come to closure yet, there's reason for encouragement," Mr. Scowcroft said in an interview on the Cable News Network.
Mr. Scowcroft, speaking to reporters while with the president in Kennebunkport, Maine, said: "I'm encouraged, but I'm not optimistic."
He added, according to the Associated Press, "We made a proposal. The Soviets have not accepted our proposal but [have] come a long way to it."
Yesterday had appeared to be the make-or-break day for Mr. Bessmertnykh's current visit, which had already been extended by a day.
Mr. Baker and Mr. Bessmertnykh had held two sessions of talks by midafternoon yesterday. The Soviets then left the building, returning shortly after 5:30, when negotiations resumed.
If the two sides remain unable to reach final agreement on the arms control treaty in the renewed talks today, the scene would shift to the London summit and the two-hour lunch between Mr. Bush and Soviet President Mikhail S. Gorbachev scheduled for Wednesday.
A deal could be reached then, but probably only if the technical problems had been distilled to the point that the presidents could quickly agree or disagree.
"It is time to get it concluded and move on, but I wouldn't say there's any anxiety about doing it," Mr. Scowcroft said on CNN.
A superpower summit "is contingent on completion of negotiations on START," Mr. Scowcroft said, referring to the pact formally known as the Strategic Arms Reduction Treaty.
The treaty, nearly a decade in the making, would slash both sides' nuclear arsenals by 25 percent to 35 percent, cutting their most destructive weapons deployed on missiles, bombers and submarines.
The most difficult remaining problem, apparently, involves "downloading."
This would reduce the number of warheads on each missile, allowing each side a greater number of missiles under the overall warhead ceiling.
The United States, seeking to avoid a situation in which the Soviet Union could speedily break out of the treaty in a crisis by adding new warheads to existing missiles, wants to limit the Soviets' opportunity to download.
A second problem is how to define new types of missiles that would be allowed under the treaty.
The United States wants to avoid a situation in which the Soviets could easily add to their arsenal and so is insisting that any new types be markedly different.
A third key problem involves how to share engineering data from missile test flights, to enable each side to know the other's progress.
Washington needs this provision more than Moscow, it is argued, because the United States has more open sources of information for the Soviets to tap.