Since the 1950s the American-Israel Public Affairs Committee (AIPAC) has been the mainstream voice of the Jewish-American community and its efforts to strengthen support for Israel in Washington.

Along comes J Street, a young upstart founded last year, in part as an answer to AIPAC – perceived by many progressive American Jews to have a clear right-wing tilt, and hardly representative of those want to see a much more aggressive push towards a two-state solution to the Israeli-Palestinian conflict.

J Street, in the thick of its first national conference in Washington that began Sunday and concludes Wednesday, has attracted 1,500 attendees – above and beyond what its organizers expected. Perhaps more interestingly, it has attracted the attention of the highest levels of government and diplomacy, and has the blogosphere buzzing about what it all means for the future of US-Israel relations.

National Security Adviser General James Jones, one of the most senior US officials to address the conference, told J Street participants Tuesday that the Obama administration believes that "Israeli security and peace are inseparable." But what's been particularly noticeable is who among beltway powerbrokers is not making his way over to the conference at the Grand Hyatt. Missing is Michael Oren, the Israeli Ambassador to the US appointed by Prime Minister Benjamin Netanyahu.

After several weeks of indecision on whether to accept the invitation, Mr. Oren announced last week that he would not attend. The subtext of that decision was that J Street's policies were not in line with Netanyahu's, though they do appear to closely reflect the viewpoints on a two-state solution endorsed by Obama.

"The Embassy of Israel has communicated to J Street its views on the peace process and on the best way to ensure Israel's security," the embassy said in a statement. "While recognizing the need for a free and open debate on these issues, it is important to stress concern over certain policies that could impair Israel's interests."

The embassy also said that is was "privately communicating its concerns over certain policies" of J Street and that the embassy would send an observer to the conference and "follow its proceedings with interest.

That response did not sit well with various people in Israel, in particular Netanyahu critics who say he's dragging his feet on peace – and that he should be warmly welcoming J Street to the Washington power circuit. A number of centrist and left-wing Israeli political parties – including the leading opposition party Kadima, Labor and Meretz, as well a several other prominent pro-peace Israelis that include retired generals and the writer Amos Oz – took out a full-page ad in the Ha'aretz newspaper Tuesday, congratulating J Street on its arrival.

"We welcome your efforts to help Israel achieve sustainable peace with its neighbors and to guarantee Israel's security and future as a democratic state," the signatories said. "J Street is an important new voice in the pro-Israel community, and we look forward to working with you to advance your important agenda in the years ahead."

Having the Israeli Ambassador decline the invitation to attend the conference – when his presence is standard at the yearly AIPAC conference – is not just a small diplomatic flap, but perhaps a sign of growing pains. For more than half a century, AIPAC has had a more or less monolithic corner on what the organized Jewish community had to say about US policy in the Middle East. Though there have always been dissidents, this is the first time that activists disenchanted both with AIPAC in general and the pace of peacemaking in particular have banded together to form a single "alternative" Israel lobby.

"This is new in the sense that one can't recall a situation in which there were two organized lobbies of American-Jewish organizations which are seeking to define relationship between the US and Israel," says Peter Medding, a professor at the Hebrew University of Jerusalem who specializes in US-Israel relations.

"Looking at it historically, this is a long-delayed reaction to the fact that Israeli society became divided over what should happen with the territories" which Israel occupied in 1967, Medding says. "At the same time, what J Street is trying to do is not palatable to large sections of the American-Jewish community. And I think that the deeper issue here is (the) question, 'Who has the right to speak for us?' J Street is adding a voice to a young, energetic generation who wants something different."