A 10-year-old political impasse that had mired two previous international women's conferences in Middle East animosities was resolved late last night when the U.N. Women's Decade Conference agreed to delete a condemnation of Zionism from its final report.

The unanimous agreement came shortly before midnight on the final day of the conference. The United States and Israel had threatened to walk out if the word "Zionism" were included in the final document.

The compromise appeared to clear the way for the 157 countries at the conference to sign a far-reaching final document that includes hundreds of resolutions demanding women's rights in employment, in family life and in the governance of nations.

At the Copenhagen women's conference in 1980, the United States, along with Israel, Australia and Canada, refused to approve the final report because of language equating Zionism with racism. Twenty-two other countries abstained from approving that document.

The threat yesterday of a U.S. walkout, combined with statements by several Western European countries that they would not approve the final conference report if it made any reference to Zionism, forced the conference president, Margaret Kenyatta, to declare early in the evening what she said would be a "10-minute recess" to discuss the issue.

That 10-minute recess turned into an extraordinary, five-hour negotiating marathon on the floor of the main hall at the Kenyatta Conference Center. In a far corner of the hall, delegates representing the Soviet Union, Syria and the Palestine Liberation Organization, which had insisted on condemning Zionism, huddled with delegates from Kenya and Egypt who were pressing for a compromise.

The compromise reached in that huddle, which substituted the phrase "all other forms of racism" for "Zionism" as an obstacle to women's development, was circulated by Kenyan officials among the Third World countries whose votes control the conference. Finally, after scores of impromptu negotiating sessions, the conference was again called to order.

Kenya, which had said it would be embarrassed if the conference it is hosting collapsed over political issues, then presented the compromise that Sara Doron, head of the Israeli delegation, later called "a miracle, . . . a compromise that will erase the lies, mistakes and falsehoods" of the previous women's conferences in Mexico City and Copenhagen.

The conciliatory language was not accepted, however, until the Soviet Union and several Arab and African delegations were given the floor to denounce Israel. Boris Mayorsky, head of the Soviet delegation, condemned the "bloody crimes" of Israel, while Mahdi Terzi, of the PLO delegation, said that even though he agreed to delete the word "Zionism" from the final report, he continued to equate Zionism with racism.

Maureen Reagan, head of the U.S. delegation, called the denunciations of Zionism "an orgy of hypocrisy." The United States, she said, would never have agreed to the compromise had it known that the Soviet Union and Arab delegations would criticize Israel so harshly.

"We were lied to," the president's daughter said in a 4 a.m. meeting with reporters today, after the conference's final report had been adopted.

She said the Soviet and Arab delegations had told the United States they would not make critical statements about Israel. She added that the Soviet Bloc and hard-line Arab countries only agreed to delete Zionism from the report because "they didn't have the two-thirds votes needed under U.N. rules to pass the resolution , and they weren't going to get them."

The attacks on Israel, which included criticism of the United States for threatening the conference with a walkout, prompted Alan Lee Keyes, the U.S. delegation's spokesman on political issues here, to make an angry counterattack against Israel's critics.

"We reject the obscene notion that Zionism is a form of racism," Keyes said, his voice cracking with anger. "We believe that no matter how often that slanderous lie is repeated, none of the repetition, no amount of reiteration shall ever lead in any truth whatsoever."

While Keyes was booed roundly by the conference after his statement, both the Israelis and the Americans expressed pleasure at the willingness as of the conference to aside an issue that they said was unrelated to the "unique concerns of women."

"I haven't seen such a display of international support of Israel in years," said Naomi Chazan, a member of the Israeli delegation. "I think it came from the pent-up frustration of women who have come to these conferences to work on women's issues and who had gotten tired of seeing all their work fall apart over the word 'Zionism.' "

While the resolution condemning Zionism became the lightning rod for disagreement at the conference, there were several other areas of discord -- over the question of a Palestinian homeland, economic sanctions against South Africa and a Third World denunciation of rich countries for unfair trade practices.

None of these issues was considered important enough by any nation either to force a walkout or to prevent them from signing the final report.

The United States, along with 28 other countries, mostly Western European, abstained yesterday from voting on a resolution condemning the "coercive measures" used by developed countries against the Third World.

On Thursday, in a move that ended the unanimous agreement by which more than 350 resolutions had been approved during the two-week conference, the United States flatly refused to accept language recognizing the right of the Palestinian people to create their own state.

While saying last night that the United States stood by that position, and was prepared to abstain from any vote calling for a Palestinian homeland, Keyes added that the passage of the measure would not prevent U.S. approval of the conference's final report.