WASHINGTON — U.S. Sen. Joseph Lieberman, D-Conn., has often been able to count on strong support from American Jewish voters. But now, when Lieberman arguably needs it most, Jewish voters will have to decide whether to stick with Lieberman.

Lieberman, who became the first Jew to run on a national ticket as the Democratic vice presidential nominee in 2000 and then made his own presidential bid four years later, lost Connecticut’s Democratic primary for re-election to the Senate on Tuesday to Ned Lamont, a business executive whose campaign was based largely on what he viewed as Lieberman’s support for the Bush administration and the Iraq war.

Lieberman has vowed to continue the race as an independent. But he is expected to face strong pressure from Democratic heavyweights to drop out.

If Lieberman chooses to go forward as an independent candidate, Democratic Jews will be left with a choice between their party and their elder statesman.

“It could be ugly,” said one Jewish Democratic operative, who asked not to be identified. He predicted that most Democratic fundraisers and party activists will side with Lamont.

“I think you will find a lot of Democrats basically saying: ‘I like Joe, I’ve supported Joe, but we have to move on and we have to support the nominee because we need to make sure the seat stays Democratic,'” said Steve Grossman, a former Democratic National Committee chairman.

Grossman, also a former president of the American Israel Public Affairs Committee, said several weeks ago that he would back Lieberman, but reversed course Wednesday, saying he would help Lamont if asked.

The question for party loyalists is more than academic. Because Lieberman is likely to garner strong support among Republicans and independents in the state, he has a good chance of maintaining his seat as an independent candidate.

But at the same time, he will need more resources because he will be running without support against a self-financed, wealthy opponent.

So Democratic Jews will have to choose wisely, knowing that whichever way they go, they could end up angering the party or a sitting senator.

Although he became a Jewish celebrity as the 2000 vice presidential nominee, Lieberman learned in 2004 that his religion would not necessary translate into votes or financial support from Jews.

During his presidential run, Lieberman heavily targeted Jewish donors, but did not get the depth of support from the community that many had assumed he would. Fundraisers said that while Jewish donors were happy to see a Jew run, his politics were too conservative for some of them.

Indeed, even longtime Lieberman supporters chose to back the senator’s presidential bid while also giving to other Democratic candidates, either because of historical relationships or a desire to support a candidate with more potential.

Officials in the Lieberman camp said it was too soon to tell whether he would actively court Jewish votes or money, but that they expect to garner support from his traditional base.

“At a moment like this, when it’s a very difficult challenge, you learn who your friends are,” said Dan Gerstein, a senior adviser to Lieberman. “The Jewish community has been very supportive of Joe Lieberman and we expect them to continue to be so.”

That tug of war between support for a longtime friend and what is best for the party is likely to play out again this time around.

“I think it will split,” said Ira Forman, executive director of the National Jewish Democratic Council. “This would be an easier question if Lamont was spouting anti-Israel rhetoric.”

The conflict is heightened by the fact that Lieberman has become increasingly out of touch with mainstream Jewish political views. His support for faith-based initiatives and the Iraq war runs counter to the views of many liberal Jews, and Lamont’s perspectives may be more appealing to some Jewish voters.

Connecticut Jews make up some 111,000 of the state’s 3.4 million people, or a little more than 3 percent of the population, according to the Jewish Virtual Library. Democratic fund-raisers and supporters said Lieberman’s primary loss was his own fault because he was slow to acknowledge discontent among his constituents over the war and did not put enough effort into the primary campaign until it was too late.

“Joe mishandled this badly,” Grossman said. “He did not see this coming, and he did not heed the warnings that he should take this seriously. He was not a catalyst for community conversation.”

Lieberman faced similar criticism in 2004 when he made a bid for the presidency. Party players then said he did not work hard enough for their vote, assuming it was his for the taking after being the party’s vice-presidential nominee four years earlier.

Grossman said Lamont’s support for Israel in recent weeks showed he could take tough positions against his own base of liberal activists and bloggers, many of whom have called for Israeli restraint and an immediate cease-fire in the war with Lebanon.

Lamont said last month in a campaign statement that “it is not for the United States to dictate to Israel how it defends itself.” He said the Bush administration should be more engaged in the Middle East, while not imposing a resolution on Israel.

A the same time, Lamont’s campaign has been almost singularly focused on Iraq, and some Connecticut Jewish voters have said they do not know enough about his views to effectively weigh him against Lieberman.

The Democratic Party establishment will have to support Lamont, its nominee, party officials said. And unlike some, who will try not to choose sides, party elders will have to actively campaign for him.

Since the seat is unlikely to fall to a Republican — Lieberman has said he will continue to caucus with the Democrats if elected as an independent — the Democratic Party is not likely to shell out major dollars on the race.

“It’s clear that all of the Democratic Party leaders are going to endorse and work for the Democratic nominee,” said the party official who did not want to be identified. “Yet at the same time, because it’s a safe Democratic seat, how hard they work and whether any money goes into this race is yet to be decided.”

Lieberman, who is religiously observant, is likely to be able to rely on some small Jewish constituencies, including Republican Jews, the Orthodox and voters who rate Israel as a primary issue.

Republican Jews and the Orthodox are likely to back Lieberman in part because of some of his social policies, which are seen as more conservative than most Democrats. Even some partisan Republicans may back Lieberman, because the race lacks a strong Republican challenger.

“If he runs as an independent, I think you’ll find that even committed Republicans like myself will do everything in their power to support him,” said Jeff Ballabon, an Orthodox Republican political activist.

Lieberman’s support of Israel will probably help him as well, especially since many pro-Israel voters, including supporters of AIPAC, the pro-Israel lobby, tend to back incumbents, and Lieberman has been an outspoken backer of the Jewish state.

Some are also likely to rally around Lieberman because of his faith, and the desire to support a fellow Jew when he is on the ropes.

But in the end, most Jewish voters, and out-of-state donors, will be left with a political version of Sophie’s choice.

“As a Democrat who believes that the political process has rules, and if you submit yourself to the electorate, you should accept the wishes of the electorate, that’s what creates a huge conflict in my mind,” Grossman said. “My guess is many Jewish activists will be equally conflicted.”

Matthew E. Berger is a reporter for Congressional Quarterly.