The Obama Administration's call for Israel to sign the Nuclear Non-Proliferation Treaty (NPT) could jeopardize a 40-year-old secret agreement between Washington and Jerusalem and make Prime Minister Benjamin Netanyahu's May 18 meeting with President Obama a difficult one. Speaking Tuesday at a United Nations meeting on the future of the NPT, Assistant Secretary of State Rose Goettemoeller flatly declared:

"Universal adherence to the NPT itself – including by India , Israel, Pakistan and North Korea – also remains a fundamental objective of the United States."

Since a September 25, 1969 summit between President Richard Nixon and Prime Minister Golda Meir, the United States and Israel have had this understanding: Both nations would keep quiet about Israel's nuclear weapons. Israel would refrain from testing them, while the United States would not pressure Israel to sign the NPT, which limits nuclear weapons to five countries: the United States, France, Britain, Russia, and China.

Today, however, the Obama Administration is seeking talks with Iran over its nuclear program, and Tehran says there can be no progress so long as the Islamic Republic is treated differently from Israel. On Monday, Iranian Deputy Foreign Minister Mohammad Ali Hosseini said that nuclear cooperation by the United States, Britain and France with Israel occurs "in total disregard with [sic] the obligations under" the NPT and remains "a source of real concern for the international community, especially the parties to the treaty in the Middle East."

Faced with Iranian stonewalling, the Obama Administration has been sending mixed signals about how far it is prepared to go in pressuring Israel. Goettemoeller declined to say whether the administration would press Israel to sign the NPT. Washington Times reporter Eli Lake got mixed signals when he put the question to administration officials: A "senior White House official" described Israeli and Iranian nuclear programs as unrelated "apples and oranges." But, asked whether the Obama Administration would press Israel to join the NPT, the official replied: "We support universal adherence to the NPT. [It] remains a long-term goal." When asked the administration's position on the 1969 understanding, the senior White House official had no comment.

If Obama leans on Netanyahu over signing the NPT, look for the Israeli leader to push back – hard. During the 1998 Wye River peace negotiations, Netanyahu sought a personal commitment to the Nixon-Meir understanding from President Clinton because of Israeli concerns about a treaty barring the production of fissile materials that can be used to make nuclear weapons. Israel was worried that the treaty might oblige it to allow inspections of its Dimona facility. Aluf Benn of Ha'aretz reported on a letter Netanyahu sent Clinton during the Wye River talks which contained the following passage: "We will never sign the treaty, and do not delude yourself, no pressure will help. We will not sign the treaty because we will not commit suicide."

In an appendix to the Wye River accord, President Clinton sent a letter to Netanyahu promising in writing that the United States would preserve Israel's strategic deterrence capabilities and ensure that they would not be damaged by future Mideast arms-control initiatives.

Read more about the U.S.-Israel nuclear weapons issue here.