The U.S. Ambassador to the U.N. Susan Rice appeared on MSNBC this morning defending the Obama administration’s Iran policy even as she tempered her optimism for a breakthrough in upcoming talks. “The window is finite,” she said, urging Iran to “come serious, ready to deal.” Rice remarked that going to war with Iran over its nuclear program “premature,” and added that “a strike is not going to end the program in perpetuity. It may set it back a year or two.”

Along with allies such as France, Rice was skeptical talks can work:

RICE: You don’t trust them [Iran]. But we test the proposition, which is very much in our interest, that with this mounting and crippling economic pressure, the extraordinary sanctions that we have put in place internationally and on a national basis, that Iran is really starting to feel the heat. …

Let me be very be clear and repeat what the president said this week: We have a clear cut policy of preventing Iran from acquiring a nuclear weapon, not containing a nuclear Iran. We think the best and most permanent way of accomplishing that is through a combined policy of intensified sanctions and pressure, which we are mounting, with the opportunity for Iran to resolve these issues diplomatically. If they take that opportunity and give up their program through a negotiated solution, that’s the best case scenario. …

if they don’t accomplish that through a negotiating process in short order, then of course as the president said, all options remain on the table.

Watch Rice concisely lay out the Obama administration’s policy:

The repudiation of “containing a nuclear Iran” tracks with Obama’s speech to the American Israeli Public Affairs Committee this weekend, where he said a nuclear-armed Iran would pose a threat to the U.S. and its allies, and the international non-proliferation regime:

A nuclear-armed Iran would thoroughly undermine the nonproliferation regime that we’ve done so much to build. There are risks that an Iranian nuclear weapon could fall into the hands of a terrorist organization. It is almost certain that others in the region would feel compelled to get their own nuclear weapon, triggering an arms race in one of the world’s most volatile regions.

Rice added that the Iranian regime has engaged in “crazy behavior” like calling for Israel’s destruction, but echoed Obama and the top U.S. military officer by noting that “we have seen Iran make decisions based on their calculation of their interest.” Faced with pressure, she said, the regime has “changed course,” raising hopes of a “real possibility that with mounting and crippling economic pressure, that Iran may change course and come to the table seriously.”

The IAEA and U.S. intelligence officials have said that Iran is on a path toward a nuclear weapons program. Indeed, the AP reported yesterday that the U.N. nuclear agency is concerned that Iran may have tried to cleanse traces of nuclear material from a site suspected of focusing on alleged weaponization aspects of its nuclear program. But the IAEA and U.S. intelligence have also said that so far, Iran has not yet decided on whether to build nuclear weapons.