Mr Yushchenko said only a collective security pact could protect Ukraine
Ukraine has said it is ready to make its missile early warning systems available to European nations following Russia's conflict with Georgia.
The foreign ministry said Moscow's abrogation earlier this year of an accord involving two tracking stations allowed it to co-operate with others.
President Viktor Yushchenko said his country could ensure its sovereignty only through collective security.
Last week, Kiev limited the freedom of movement of Russia's Black Sea Fleet.
The move came after several of the fleet's warships, based at Sevastopol in Ukraine's Crimea's peninsula, were deployed along the Georgian coastline.
Moscow denounced the restrictions as anti-Russian and said its military commanders would answer only to the Russian president.
In a statement, Ukraine's foreign ministry said that because the country was no longer party to the 1992 agreement with Russia on the use of its radar stations, it could now "launch active co-operation with European nations".
This might include "the integration of Ukrainian elements of missile early warning and space control systems with those of foreign countries that are interested in gathering space data", it said.
Earlier this week, President Yushchenko issued a decree putting an end to Ukraine's participation in the accord in view of Russia's abrogation of it.
He said the situation was unprecedented and showed that his country could only ensure its national sovereignty through collective security.
Only that, he said, "could prevent any actions like those which occurred on 7-8 August at first in South Ossetia, and then in other regions of Georgia".
BBC diplomatic correspondent James Robbins says the decision is evidence Ukraine is now more desperate to embrace the West as its fear of Russia intensifies and Moscow seemingly becomes more determined to prevent any neighbouring states from joining Nato.
Russia clearly sees Nato as America's sphere of influence, despite US President George W Bush's insistence that it is a purely defensive alliance of sovereign democracies, our correspondent says.
Increasingly, the events of the past 10 days demonstrate Russia has gone back to arm-wrestling with its neighbours and the West after the immediate post-Soviet years, when it felt too weak, he adds.