A breakthrough agreement between Russia and Estonia on the pullout of Russian troops hit a diplomatic hitch Wednesday when the two governments failed to sign an accord on the dismantling of a nuclear reactor.


Russian Foreign Minister Andrei Kozyrev was quoted by Interfax as saying the signing delay was technical and the Estonian side needed to consult further on the text of the agreement.


As part of a package negotiated in a marathon five-hour meeting Tuesday between Presidents Boris Yeltsin and Lennart Meri, Russia promised to dismantle a nuclear reactor at its Paldiski naval base in Estonia.


Meri won Yeltsin's agreement to pull out Moscow's remaining troops by the end of August in exchange for a promise to give more rights to Russian military pensioners living in Estonia.


Yeltsin on Wednesday described his talks with Meri as the longest he had held with any president. "It was a difficult conversation, a very difficult conversation," he said at a Moscow airport before leaving on a three-day trip to Siberia. "We spent five hours -- I haven't devoted that much time to any other president."


Yeltsin said he had threatened at one point to leave the troops in Estonia indefinitely unless Meri agreed to link the pullout to the rights of ex-Soviet military pensioners in the Baltic state.


"Russia adopted a very tough position," Yeltsin said. But he hinted that he had come under heavy pressure from the West to agree on a withdrawal, saying he had received letters from President Bill Clinton and Chancellor Helmut Kohl urging a speedy pullout.


"Estonia succeeded in waking up the West," Yeltsin said. Moscow has already withdrawn its troops from Lithuania and promised to pull out from Latvia by the end of August. This left the estimated 2,000 troops in Estonia as the major obstacle to an improvement in relations with Russia's Baltic neighbors, all of which won independence from Moscow in 1991.


Full details of the agreement on pensioners' rights were not available, but Estonian officials in Tallinn told journalists Meri had made no major concessions to Yeltsin. They said no changes in Estonian law would be required and only people born before 1930 -- now aged 64 or over -- would be considered pensioners.


The estimated 9,000 retired Russian officers in Estonia have been at the center of a wider disagreement over the status of the much larger Russian-speaking minority there, viewed by many Estonians as occupiers.


Endel Lippmaa, opposition member of parliament for the right-wing Coalition Party, said Meri would face "a large-scale conflict" with parliament over the deal with Yeltsin.