By STEVEN LEE MYERS
WASHINGTON, Aug. 28 -- The Pentagon and the State Department are sharply divided over how far work on a limited national missile defense system could proceed before the United States would be required to give formal notice that it was violating a crucial arms control treaty with Russia.
Officials in the Pentagon and State Department said that disagreement within the administration was a primary reason for Defense Secretary William S. Cohen`s delay in making a recommendation to President Clinton this month on the project.
The debate has focused on the point at which construction of the missile system, which involves elaborate radar installations, would violate the Antiballistic Missile Treaty of 1972, which lies at the heart of the arms controls built up over the cold war.
The Russians have steadfastly refused any changes in the pact to permit elaborate new radar installations, fearing that they would lead to a larger system that would undermine Russia`s strategic nuclear force.
Officials from both agencies said Mr. Cohen was wrong when he told the Senate Armed Services Committee last month that administration lawyers had reached a consensus. Mr. Cohen said then that there was agreement that building a crucial radar station in Alaska could continue until 2002 before the United States would violate the treaty.
That represents just one of three interpretations drafted by administration lawyers, the officials said. But senior policy makers at the State Department and the National Security Council are strongly opposed, the officials added. The opponents contend that this interpretation would be overly aggressive and unilateral, and would surely anger the Russians and European allies.
A Pentagon spokesman, Rear Adm. Craig R. Quigley, said Mr. Cohen and his aides declined to discuss his Senate testimony. Mr. Cohen is the administration`s leading advocate of building missile defenses.
Aides to President Clinton declined to discuss the internal debate but confirmed that officials were considering several options and that Mr. Cohen`s statement last month did not reflect a consensus view. "It is true that there are a number of options available to the president," said P. J. Crowley, a spokesman for the National Security Council.
The question of when the United States would violate the treaty is a pivotal one that Mr. Clinton has to answer before approving even limited steps to begin building a radar station on Shemya Island at the western edge of the Aleutians. The Russians would surely object to the United States and its allies.
Mr. Cohen is now widely expected to make a recommendation to Mr. Clinton in a few weeks on how to proceed. But the officials said the legal questions could delay a decision to move ahead further.
The division is so sharp that Mr. Clinton may be forced to choose among conflicting advice, if he decides to move ahead at all.
"This is really squishy business," a senior military officer said. "Smart lawyers can disagree."
Under the Pentagon timetable, the first contracts for the Alaska radar work, as well as a site for the missile interceptors, would have to be awarded this year so that work can begin next spring and a working system can be in place within the administration`s goal of 2005.
Intelligence officials have warned that the United States could face a threat from some countries, including North Korea, by then. There is universal agreement that building the radar site would amount to a treaty violation. The administration had hoped to negotiate amendments with the Russians that would permit the limited system now being developed, but Moscow has refused.
Officials had previously said Mr. Clinton would decide this summer on deploying a system. But with the Russians objecting and even the allies expressing concern, the officials have signaled that Mr. Clinton simply planned to decide whether to move ahead with an initial development. He would leave a final decision to deploy -- and break the treaty -- to the next administration, whether that of the Democratic nominee, Al Gore, or the Republican, George W. Bush, who has advocated a much more encompassing system.
That is why the legal interpretations have become so important, because each interpretation sets a different moment when Mr. Clinton must, as the treaty requires, give the Russians six months` notice of American intent to withdraw from the antimissile restrictions.
At the White House request, State Department and Pentagon lawyers have drafted the three interpretations of the treaty that, in their view, would let some work begin without breaking the treaty.
In his appearance before the Armed Services Committee on July 25 and at a news conference the next day, Mr. Cohen said that the administration`s lawyers had reached a consensus that the United States would not violate the treaty until workers had laid rails to support the Shemya radar, a move scheduled for 2002.
Mr. Cohen emphasized that Mr. Clinton had not yet made a decision. But at the news conference he added, "There is a consensus that until such time as the construction is under way that would lay the rail, so to speak, for the actual radar being deployed there, that would not constitute a breach."
Defense and administration officials said Mr. Cohen, the lone Republican in the cabinet was expressing his support for the most liberal interpretation of the treaty. That view, the officials said, is being challenged by senior aides to Secretary of State Madeleine K. Albright, including the under secretary of state for arms control, John D. Holum, who is the chief arms control negotiator.
"You have to have an aggressive interpretation of the treaty to argue that the rails are the point at which you would be in violation," a senior administration official said.
All the lawyers` interpretations would overturn a legal understanding dating from the Reagan administration that even the most minimal steps to build parts of a missile defense, including pouring concrete, would breach the treaty. For years in the 80`s, Reagan aides insisted that a half-built radar station near Krasnoyarsk in Siberia violated the treaty and eventually forced the Russians to halt work there.
The second interpretation holds that the United States would be in violation at the point workers begin pouring concrete, which is scheduled to begin in May. Given the fact that the treaty requires either the United States or the Russians to give six months` notice of an intent to build, Mr. Clinton would have to then notify the Russians by December, just as his second term ends.
Officials have said Mr. Clinton is loath to be the president who brings an end to the ABM Treaty, which has been strongly supported by arms control advocates since it was negotiated in the Nixon administration.
The third interpretation argues that a violation would not occur until the concrete foundation for the radar site is complete. That is expected later next year or even in 2002, depending on weather and other potential delays. That would leave the decision on breaking the treaty to the next president.
The senior administration official said the question was proving especially difficult, because the treaty does not specify what exactly would amount to a violation. "There is some room for legal interpretation," the official said. "But I think it`s fair to say that not all of the options are equally defensible."
Opponents of the proposal said moving ahead -- while arguing that the first steps toward a missile defense would not be a violation -- would amount to a diplomatic disaster.
The Pentagon schedule has increasingly been called into question because of test failures and delays in building a booster rocket for the missile interceptors. "If the technology isn`t there, you don`t have much of a choice," one official said. "If you can foresee that the system won`t be ready until 2006 or 2007, why would you push it now?"