J Street has lined up plenty of high-profile speakers for its first major conference, but the new and controversial self-described "pro-Israel, pro-peace" lobby is looking to add one more prominent name to the guest list.

The organization -- which has backed U.S. pressure on Israel (and the Palestinians), criticized Israel’s invasion of Gaza and criticized more established pro-Israel groups -- wants Michael Oren, the U.S.-born and raised Israeli ambassador to Washington, to attend and address its first major conference at the end of this month.

Oren is undecided.

"A decision about his participation or the embassy's participation will be taken soon," his spokesman, Jonathan Peled, told JTA. "We will have to deliberate this week."

Peled said that what he told The Jerusalem Post last week still stands: Some of J Street's positions "impair" Israel's interests. He would not elaborate, except to say that this has been conveyed to J Street officials in private conversations.

Jeremy Ben-Ami, J Street's founder and executive director, is not taking no for an answer.

"Your attendance -- even to clarify some of our areas of disagreement -- will be respectfully welcomed, and we promise you an open hearing as we hope and expect you will welcome us at the Embassy one day to present our views and opinions in that same spirit," Ben-Ami wrote in an open letter released this week.

J Street sent a private invitation to Oren on July 13.

Oren's presence would lend an official Israeli imprimatur at a time when J Street’s harshest critics are painting the group as undermining Jewish unity and working in tandem with Israel’s enemies. Most recently, some critics played up the fact that a handful of J Street donors -- among thousands -- has ties with Arab countries and Iranian expatriates opposed to sanctions against Tehran.

Such efforts to delegitimize the organization appear to have failed, with 160 congressional lawmakers endorsing its conference. The slate of scheduled speakers includes several former top Israeli officials.

In addition, Rabbi Eric Yoffie, who leads the country’s largest synagogue movement, the Union for Reform Judaism, is co-chairing the main event -- a town hall meeting on Israel's relationship with American Jews. U.S. Reps. Robert Wexler (D-Fla.) and Jan Schakowsky (D-Ill.), leaders in Congress' unofficial Jewish caucus and close to President Obama, are taking part in a panel that examines how one to expand the definition of "pro-Israel" on the Hill.

Most notable, perhaps, is the participation of Yoffie, who tussled earlier this year with J Street over its equivocation over naming Hamas as the villain in Israel's Gaza war. He told JTA that J Street’s views deserve a hearing in the wider Jewish community, and praised the group for doing more than many more established groups to promote the Israeli position of a two-state solution.

Yoffie said he would not refrain from criticizing some of J Street's positions, particularly on Iran.

"This is not an area for passivity or indifference," he said. "The stakes are too high."

Beyond securing Yoffie’s participation, J Street has made significant headway in forging an increasing level of cooperation and coordination among U.S. Jewish groups associated with Israel’s dovish camp.

Along with these successes, the organization has been growing. Eighteen months ago it had no budget and no office. Now J Street has a staff of 30, offices in Washington's K Street lobbying corridor and an annual budget of $3 million.

That's what drew Hadar Susskind, 36, to the organization. Susskind, until last month the Washington director of the Jewish Council for Public Affairs, told JTA he crossed over from the consensus-driven establishment group when he determined that J Street was here to stay.

"They are speaking for a tremendous constituency in America," said Susskind, not yet settled into using "we" in his new role as J Street’s director of policy and strategy.

Susskind, who has served in the Israeli army, said J Street attracted him in part because of its major policy goal: aggressively seeking American intervention in the peace process toward a two-state solution.

"For me, going to J Street is really about doing what is best for Israel,” he said.

Susskind said he was drawn to J Street in part because he had endured for so many years of establishment discussions about how to draw younger Jews into the pro-Israel community; J Street was doing just that, he said. The expected 1,000 conference-goers will be split into two lobbying groups -- one for university students and one for everyone else.

Susskind is an establishment "get" for a group that until recently has been depicted as an outlier by officials at more established groups, with some speaking on the record, others preferring to distribute potentially damaging information behind the scenes.

William Daroff, the Washington director of the Jewish Federations of North America, sparked a tweet war last month with J Street and its defenders when he accused the group of "standing with the Mullahs" by opposing tough Iran sanctions.

J Street says it does not oppose the sanctions that would further isolate Iran for its suspected nuclear weapons program, but thinks implementation of such measures at this time would be "counterproductive."

Daroff told JTA that J Street has developed better PR chops -- condemning, for instance, Iranian President Mahmoud Ahmadinejad for denying the Holocaust and opposing an organized effort to shame the Toronto International Film Festival for celebrating Tel Aviv's centennial.

Still, he added, these were easy calls. J Street, Daroff said, has not yet defended Israel when it is unpopular to do so.

"I think that J Street's voice has some resonance on the Hill because to a large degree” it is “in sync with the Obama administration" on pressing for renewed talks and a robust U.S. peacemaking role, he said. "The question is when and if the Obama administration shifts direction, would J Street still be relevant?"

J Street has yet to get a toehold among Republicans -- the GOPers appearing at the conference are in the "exception proves the rule" category.

Rep. Charles Boustany (R-La.) is an Arab American, and former Nebraska Sen. Chuck Hagel left Congress in part because he was disillusioned with his party's foreign policy, including on the Middle East.

And despite its success in lining up former Israeli officials, J Street was turned down by Tzipi Livni, the Israeli opposition leader, who even declined to address the event by video message.

J Street critics say the organization muddies the waters by presenting multiple, conflicting voices on important topics when a unified voices is needed, at least in Washington.

"Those Jewish Americans who share a deep concern for Israel's trials and travails have the right, even the duty, to express their criticism within the Jewish community, the public at large, pretty much anywhere -- except before the administration and Congress," Chuck Froelich, a former deputy national security adviser to Israel's government, wrote this week in The Jerusalem Post. "There we have to present one voice -- not 'pro' every Israeli policy, but united, unswerving support for Israel and a strong U.S.-Israel relationship."

AIPAC may have made mistakes in the past, but is still the pre-eminent pro-Israel voice, he wrote.

"If it ain't broke, don't fix it," he said.

Behind the scenes, some AIPAC backers are said to be exercised about J Street -- although with AIPAC boasting a budget of more than $60 million, J Street hardly poses a major threat.

Any establishment anxieties about J Street are unjustified, Susskind said.

"I have tremendous respect for AIPAC," he said. "They have done wonderful work strengthening” the U.S.-Israel relationship. "We need that and more, and J Street is more."