President Reagan pledged tonight that the plight of Soviet Jews who are denied the right to emigrate will remain in the forefront of U.S. foreign policy and human rights concerns.

In a message read to the opening session of the third world conference on Soviet Jewry by Jeane J. Kirkpatrick, the U.S. ambassador to the United Nations, Reagan declared that no "durable progress" in overall East-West relations is possible without corresponding progress on human rights questions.

It is imperative, the president said, to convince Soviet leaders that a more flexible and humane policy toward their Jewish minority "is in the Soviets' best interest."

"We stand with you," Reagan told the conference delegates. "We will not forget them, we will firmly support their just cause."

In her remarks to the conference's opening session, Kirkpatrick charged that the Soviet Union is at the heart of an international propaganda campaign of anti-Semitism masquerading as "anti-Zionism." She said the Kremlin is engaged in "increasing persecution" of its Jewish minority and that denying Jews the right to leave the country was in "blatant violation" of international agreements it had ratified or endorsed.

More than 1,000 delegates from about 30 countries are attending the conference, the third since 1971 and the first to be held in Israel. Jewish emigration from the Soviet Union, conference officials said, has declined from more than 50,000 in 1979 to 2,688 last year.

At a news conference last night, Kirkpatrick appeared ill at ease when asked whether such a highly publicized gathering might be less effective in increasing Jewish emigration from the Soviet Union than "quiet diplomacy." Kirkpatrick was a vocal critic of the Carter administration's human rights policies, arguing that the public emphasis former president Jimmy Carter put on the issue was counterproductive.

"As you know, the argument has been made both ways with regard to Soviet Jews and other cases," Kirkpatrick responded. But she said that the Israeli government had "concluded that the cause is served better by calling attention to it" and that in this case "it is better to be guided by those who have spent a great deal of time studying the issue."