As it prepares for its first national show of force, J Street, the 18-month-old dovish lobby, is experiencing unprecedented success coupled with unexpected criticism.

An item of interest for the national and international press and a rapidly growing organizational power, J Street, which defines itself as the "pro-Israel, pro-peace lobby," has already made its mark as the leading pro-peace group in the Jewish community.

But it is still struggling to prove its pro-Israel credentials.

The latest bump in the road was the refusal of Israel's ambassador to the United States to meet with the group, citing concerns that J Street's views might harm Israel's interests. Ambassador Michael Oren's rebuke adds to a vocal choir of critics from the right that has intensified its activity approaching J Street's first national conference, scheduled to begin on October 25 here in Washington.

The official Israeli rejection of J Street was made public in a carefully worded statement issued by Jonathan Peled, the embassy spokesman in Washington. "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," Peled said. He added that the embassy had "communicated to J Street its views on the peace process and on the best way to ensure Israel's security."

Peled said that despite Oren?s decision not to meet personally with J Street, the embassy is conducting talks with the group through its public affairs department. "We decided to move ahead in a measured and cautious way," the spokesman said, adding that the embassy has yet to make a final decision on whether Oren will speak at the upcoming J Street conference.

Upon taking office as Israel's top diplomat in the United States, Oren stated that he would work to reach out to groups previously ignored by his government, including progressive organizations to the left of the mainstream Jewish community. Oren initiated a meeting with Americans for Peace Now, a group with similar views on the Middle East peace process to those of J Street. APN, however, is a member of the Conference of Presidents of Major American Jewish Organizations, while J Street is not.

In an open letter to Oren, J Street's executive director, Jeremy Ben-Ami, made a personal appeal. "Mr. Ambassador, what J Street shares in common with you far outweighs that on which we disagree," Ben-Ami wrote. He invited Oren to "argue over how best to ensure the health, safety and vibrancy of the Jewish people and of Israel for generations to come."

Shunning J Street may be a result of domestic Jewish politics as much as an expression of foreign policy. A diplomatic source told the Forward that Israeli officials received calls from Jewish organizations stating that they "have a problem" with J Street. The groups, which the source would not name, argued that J Street's criticism of other Jewish organizations should not be endorsed by the government of Israel.

Representatives of major Jewish groups contacted by the Forward denied any involvement in convincing the Israeli government not to engage with J Street.

Hadar Susskind, J Street?s new director of policy and strategy, said he still hopes Oren will attend the conference. "So often,? Susskind said, "the problem is that the ambassador is hearing people who categorize for him groups as pro-Israel or anti-Israel." He added that those who say J Street is anti-Israel are wrong, and some are "intentionally spreading falsehood" because they feel "threatened by having another voice out there." Others, Susskind argued, do so out of a partisan political motivation.

Morris Amitay, a former executive director of the American Israel Public Affairs Committee who now heads a pro-Israel political action committee in Washington, said that J Street received a "well-deserved rebuke" from the ambassador. Amitay said that Oren was ?showing good taste? in not meeting with J Street, adding that the Israeli ambassador to the United States is not obliged to meet with every Jewish group.

But Seymour Reich, a veteran Jewish leader who once was head of the Presidents' Conference, argued that disagreements with J Street's views should not deter engagement with the organization. "It would be appropriate for the ambassador to meet with J Street so each side can hear the other?s views," Reich said. He also noted that Ben-Ami was included when President Obama recently met with Jewish leaders, giving the group extra credibility.

M.J. Rosenberg, one of the leading voices in the dovish community and a senior foreign policy fellow at Media Matters, a non-profit research center, said that Oren?s refusal to meet with J Street shows a flawed reading of the Jewish communal map. "Does he think it is enough to meet with Howard Kohr and David Harris? Doesn't he understand that they are the old guard?" Rosenberg asked, referring to the heads of AIPAC and the American Jewish Committee, respectively.

J Street is expecting 1,000 participants at its conference; 160 members of Congress have signed on to the honorary host committee for the conference's gala dinner - most from the Democratic side of the aisle. During the conference, participants will also introduce the new lobby to lawmakers on Capitol Hill.

By comparison, AIPAC draws more than 5,000 participants to its annual conference, holds hundreds of lobbying meetings and hosts more than half the members of Congress at its gala event, alongside top government officials from the United States and Israel. J Street had only partial success in attracting speakers from Israel; several current and former Israeli lawmakers will attend, but none from the government or the ruling Likud party are on the list.

One keynote speaker receiving special attention is Rabbi Eric Yoffie, president of the Union for Reform Judaism. Yoffie had sharply criticized J Street this past winter for its opposition to Israel?s military campaign in Gaza.