President Reagan yesterday hailed the signing of the Israeli-Lebanese peace agreement and, in an implicit appeal for cooperation by Syria and the Palestine Liberation Organization, cited the risks for Middle East peace if all foreign forces fail to withdraw from Lebanon.

There also were indications that Reagan is about to release his hold on F16 jet fighters scheduled for delivery to Israel in 1985. Last month he announced that the planes would be held until Israel agreed to withdraw from Lebanon. Reagan said last night that consultations between the State Department and Congress about the F16s were about to begin.

Defense Secretary Caspar W. Weinberger, testifying to the House Foreign Affairs Committee, said that "the additional threat" from increased Soviet troops and weaponry in Syria has increased the need for the kind of self-defense "for which the planes were originally intended."

Reagan read a statement at the White House, standing with Secretary of State George P. Shultz, who negotiated the agreement in 17 days of shuttle diplomacy.

The accord calls for Israel to pull its troops out of Lebanon. However, it cannot be implemented until Syria and the PLO, which oppose the agreement, consent to withdraw their forces at the same time the Israelis leave.

"The risks if withdrawal fails are far greater than the risks of completing the withdrawal," Reagan said.

Nicholas Veliotes, assistant secretary of state for Mideast affairs, said that the agreement and related documents will be forwarded to Congress. But Veliotes added that some parts would remain classified.

In 1975, when then-secretary of state Henry A. Kissinger negotiated a partial Israeli withdrawal from the Sinai Peninsula, he made a secret commitment that the United States would not deal with the PLO as long as it refused to recognize Israel's right to exist.

The current secret documents are "side letters" from the United States to Israel and Lebanon relating to what State Department officials called "clarifications" and "understandings" about the agreement.

The document relating to Israel was signed there yesterday by Israeli Foreign Minister Yitzhak Shamir and U.S. Ambassador Samuel Lewis.

Shultz has denied that the United States promised Israel any aid increases in exchange for the agreement. Other diplomatic sources said yesterday that the United States has given "no quid pro quo of any sort" to Israel.

Instead, the sources said, the memorandum is intended to satisfy Israel's insistence on U.S.-Israeli understandings about key points in the accord and to make clear that its terms cannot be changed at the insistence of Syria or other Arab governments.

The sources said the memorandum spells out a U.S. understanding that Israel is not required to withdraw from Lebanon if Syria and the PLO don't. They said that it contains a U.S. promise to do everything possible to implement the agreement, including the withdrawal of all foreign forces, and a recognition that the accord does not limit Israel's right to self-defense.