MOSCOW, Oct. 15 — The two pro-Western political parties in Ukraine that united in triumph in the Orange Revolution of 2004, but then quarreled and lost control of Parliament, reached a coalition agreement on Monday to retake power.
Hours after the official results of last month’s parliamentary balloting were announced, the two parties declared they had enough votes to ensure that Yulia V. Tymoshenko, a former prime minister, would again assume the post with the backing of her sometime ally and rival, President Viktor A. Yushchenko.
Ms. Tymoshenko, who has vowed to move Ukraine closer to the European Union and further from Moscow’s orbit, seemed to acknowledge on Monday that her earlier, brief tenure as prime minister had been troubled.
“We have drawn conclusions about what happened in previous years,” she said. “We firmly know what to do, we firmly know how to do it and with which team.”
Mr. Yushchenko, the hero of the Orange Revolution who has suffered a stark decline in popularity because of political instability, issued a statement calling on all the major political parties to work together.
“This will give the country an opportunity to get out of the bewitched circle of crises and conflicts in the power structures, and open a path for progress,” he said.
The agreement is tentative, because Ms. Tymoshenko will not formally become prime minister until the new Parliament meets in coming weeks. The two leaders have a history of reaching deals that quickly collapse, but their aides insisted that this one would last.
For now, the pact represents a political resurrection for Ms. Tymoshenko, whose spirited speeches made her a symbol of the Orange Revolution and one of the best-known politicians in Eastern Europe.
The revolution erupted after Mr. Yushchenko lost a presidential election that was deemed to have been stolen by supporters of his opponent, Viktor F. Yanukovich, who was strongly backed by the Kremlin.
Last year, Mr. Yanukovich took advantage of feuding between the president and Ms. Tymoshenko to mount a strong showing in elections and return to power as prime minister.
He was still overtaken this year, though, despite his efforts to moderate his apparatchik image with the help of an American political consultant.
While the president sought reconciliation, Mr. Yanukovich issued a statement in which he did not mention Ms. Tymoshenko by name but attacked how the campaign had been conducted and criticized politicians “who put their ambitions and interests over the national interests.”
Mr. Yanukovich notwithstanding, it is the prickly relationship between Mr. Yushchenko and Ms. Tymoshenko that will now once again take center stage. Their coalition has only a small edge in Parliament, and defections could cause more political disorder.
Final election tallies released Monday showed that Mr. Yanukovich’s Party of Regions won the most seats in Parliament, with 175, followed by Ms. Tymoshenko’s party, Bloc Tymoshenko, with 156, and Mr. Yushchenko’s party, Our Ukraine, with 72.
Parliament has 450 seats, and the two pro-Western parties will have 228 seats. The coalition could still attract 20 more seats from one of the smaller parties.