WASHINGTON -- Russia's refusal to negotiate changes in its 1972 Anti-Ballistic Missile Treaty with the United States played a key role in President Clinton's decision to delay the initial phases of construction for a national missile defense system, leading U.S. newspapers reported Sunday.

The Washington Post and The New York Times said Clinton's move stemmed from Russia's insistence that even initial construction of a missile shield would be in violation of the 1972 treaty.

The Post said Clinton's decision had actually been shaped by events as far back as January when Moscow first made clear it would not be willing to amend the treaty.