Russia may be on the verge of accepting the principle of limited anti-missile defenses as a protection against attack, a top Bush administration official says.

No agreement has been reached, no deadline set, the official said Wednesday.

But Russia has begun to share American apprehensions about the growing nuclear capability of several countries, and is particularly concerned about Pakistan, the official said.

In fact, President Vladimir Putin has interceded with North Korean leader Kim Jong Il to urge him to curtail or even abandon his push to develop long-range missiles, said the official, who spoke Wednesday on condition of anonymity.

Yet, despite urgent U.S. pleas, Russian companies still provide Iran with technology for weapons of mass destruction, the official said. The technology could help Iran in its programs to develop chemical, biological and especially nuclear weapons, he said.

U.S.-Russian negotiations will continue this month, with Secretary of State Colin Powell, Undersecretary of State John Bolton and Undersecretary of Defense Douglas Feith talking separately with Russian delegations.

Putin is scheduled to meet with President Bush in Crawford, Texas, in November, but there is no suggestion a deal will be struck by then.

Indeed, Oleg Chernow, deputy secretary of Putin's security council and point man on missile defense, told The Washington Post "it's impossible" that an agreement would be reached that quickly.

In an interview appearing in Thursday's editions of the Post, Chernow said Russia considers the Bush-Putin meeting to represent an "intermediate stage" in talks that probably will last at least until September 2002.

Russia wants to retain the 1972 Anti-Ballistic Missile treaty, which prohibits national defenses against missiles. Bush has declared the treaty a relic of the past and made clear it will be swept aside if he decides it conflicts with U.S. interests.

U.S. tests are expected to run counter to the treaty within months.

There may be a basis for compromise in a U.S. offer to share technology with Russia, to develop jointly a system to warn of imminent attack and to agree to cutbacks in nuclear weapons stockpiles.

The extent of U.S. reductions would be guided by a Pentagon review already under way.

The Pentagon is expected to conclude by this fall how many nuclear weapons the United States needs. Results of the overall review of U.S. military strength are due by the end of the year.

In any event, the official said, while progress is slow, the Russians are beginning to accept the idea of limited defenses against smaller potential enemies.

Meanwhile, a Pentagon official said Wednesday that a U.S.-Russian center aimed at avoiding accidental missile launches, already three years on the drawing board, won't open for at least another year.

Plans to convert a building on the outskirts of Moscow into a joint early-warning center are hung up on Russia's insistence the United States pay taxes on the equipment it takes into the country and accept liability for the construction, said Philip Jamison, deputy director of the Defense Department office on international security.

"It essentially boils down to diplomatic issues," he told a seminar at the Cato Institute. Jamison said the center could be open for testing at the end of 2002 if those matters can be resolved within the next two months.

When plans for the center were announced in September 1998, then-President Clinton said it was aimed at averting "nuclear war by mistake." Officials said that because Russia doesn't have money to properly maintain its warning system, it could mistakenly think the United States had launched a nuclear missile and retaliate.