By Paul Reynolds, World Affairs Correspondent
"A US decision to drop plans to base an anti-ballistic missile defence system in Poland and the Czech Republic would be a huge shift in American foreign and defence policy by the Obama administration.
The decision was reported in the Wall Street Journal and official word is expected during the day.
Implications
The implications of such a move would include the following:
First, it would be a major signal, which has followed a number of others, that the United States is adopting a far more cautious foreign policy under President Obama than it did under President Bush.
President Bush was determined on the European-based system and agreements had been reached with Poland to base 10 anti-missile interceptors there and with the Czechs for them to house the system's radar.
President Obama ordered a review when he came into office and apparently does not see the need for such a hurry. His experts seem to be telling him that Iran - the cause of all this deployment - is not after all quite so advanced in its ballistic missile technology.
The second effect would be on US relations with Russia. Here the picture will be mixed. The Russians will be pleased and therefore relations will be eased. The Russians had claimed the system might be a threat to them, though the US said it would not. The US felt that the Russians were simply making an excuse to meddle in the affairs of their near neighbours.
But the Russians might also feel triumphant and conclude that their tough approach is one that brings respect and results.
Thirdly, this might indicate that the Obama team will be looking as sceptically at claims that Iran is developing an actual nuclear weapon. That could mean a reluctance to attack Iranian nuclear plants without rock-solid information, though this would not necessarily stop the Israelis from doing so.
Fourthly, the Polish and Czech governments might have mixed feelings. They had invested considerable capital in agreeing to the system. Some hardliners might feel let down. Others might be relieved. There will be debates about the long-term US commitment to Europe.
Fifthly, on the military side, this would herald a shift of emphasis in the whole US anti-missile defence strategy.
According to the Wall Street Journal account, the emphasis will now be on regional defence. The Israeli example might be a good one. The US is co-operating with the Israelis on the Arrow anti-missile missile and on a shorter range missile interceptor known as David's Sling.