Senator Obama’s call Tuesday for a world free of nuclear weapons came at such an inapt time that it couldn’t have been a coincidence. “Here’s what I’ll say as president,” Mr. Obama pledged. “America seeks a world in which there are no nuclear weapons.” President Reagan, too, sought a world in which there are no nuclear weapons. But, as the saying goes, Mr. Obama is no Ronald Reagan. The senator argued that by not openly leading a campaign to end nuclear weapons America is “giving countries like Iran and North Korea an excuse.” The only thing he accomplishes by this kind of talk is to lend credence to the argument that all nuclear weapons are the same regardless of who possesses them.

It doesn’t take an atomic scientist to figure out where that argument leads. The fact is that it makes an enormous difference what kind of state possesses nuclear weapons. Does anyone really believe that the dangers associated with allowing the Iranians to acquire nuclear weapons carry the same weight as those associated with Israel nuclear weapons? Israel is not supporting terrorist groups, such as the operations that Iran is supporting in Hamas and Hezbollah. Israel is not threatening the Arab regimes in the Persian Gulf. Israelis are not aiding the killing of American and NATO troops in Iraq and Afghanistan.

Mr. Obama is playing right into President Ahmadinejad’s hands. How much of a stretch is it to go from a call for putting an end to all nuclear weapons to agreeing with Iran that there is equivalency between the Iranian nuclear weapons program and, to take one example, Israel’s or Britain’s or France’s or our own? America, moreover, is in the midst of a diplomatic and economic campaign to stop the Iranian nuclear weapons program. President Bush has chosen the multilateral path that, according to his critics, including Mr. Obama, he eschewed in the run-up to the Iraqi war.

Mr. Obama’s words can only be — and will be — seen as the weakening of the American will to ensure that Iran does not get the bomb. The connection between Mr. Obama’s far-reaching statement on nuclear weapons policy and Iran was highlighted in Tuesday’s Washington Post in a dispatch, “Sanctions Won’t Stop Tehran,” by Selig Harrison, who directs the Asia Program at the Center for International Policy. He argues that Iran has set conditions for a “grand compromise” with America that render such a deal impossible. The conditions go beyond requiring our administration to take the path advocated by Senator Obama and many Democrats, namely to abandon economic sanctions and talk of war and enter direct negotiations with the mullahs.

Mr. Harrison writes that even if America “drops its insistence on the suspension of uranium enrichment as a precondition for dialogue,” Iran would not agree to “the terms for denuclearization accepted by North Korea” — a no-attack pledge, normalized economic and diplomatic relations, economic aid, and removal from the State Department list of terrorist states. Iran, he says, would pocket all that and still insist that Israel freeze activity in its alleged nuclear reactor and that America agree to a ban on it using nuclear weapons in the Gulf. It is clear that such a demand would not be met by Israel.

Israel’s nuclear might, if indeed it exists, would be a strategic, stabilizing force that cancels out the Arab advantage in numbers of men and weapons. The Jewish state does not rely only on its nuclear umbrella: as fighting in the summer of 2006 in Lebanon and the Gaza Strip underscored, most battles require Israel to maintain a substantial edge in conventional military terms. Mr. Obama may be trying to draw attention to himself as a “visionary” leader, in contrast to Senator Clinton, who continues to lead him in most polls. But his remarks distract attention from the need for a serious discussion about nuclear proliferation.

Such a discussion will have to take account of the January 4 Wall Street Journal op-ed piece on which Mr. Obama based his plan, which, if for no other reason than its provenance, deserves attention. “A World Free of Nuclear Weapons” was co-authored by a bi-partisan group of diplomatic and security heavyweights led by State Secretaries Kissinger and Shultz, Defense Secretary Perry, and Senator Nunn. The authors argue that we are on “the precipice of a new and dangerous nuclear era,” because of the threat of nuclear proliferation and “the likelihood that non-state terrorists will get their hands on nuclear weaponry.” Indisputable. But what to do? If the argument is that America will be made safer by taking nuclear weapons out of the hands of America, Israel, or Britain, our sense is that, whether the person doing the talking is Senator Obama or more conservative foreign policy heavyweights, the American people are not going to be easily convinced.