NEW YORK — This week, the birthright israel program is celebrating the 100,000th participant on its free, 10-day trips to Israel. But one person who’d hoped to be among the thousands of young Jewish adults joining this summer’s festivities won’t be.

That’s because the woman, a 26-year-old resident of California, was dropped from the program last week when birthright officials learned that after participating in their program, she planned to join another group in a trip through the Palestinian territories.

Birthright is standing unapologetically behind its decision on the woman, Sierra, who has denied interview requests and asked that her last name not be used.

Its program is meant to build Jewish identity, officials say, and if participants are using the trip for other purposes, birthright reserves the right to turn them away.

But a co-founder of Birthright Unplugged — the name of the program in the Palestinian territories, a clear dig at the birthright israel brand — says that by denying Sierra a ticket to Israel, birthright simply confirms the need for alternative programs.

But while Birthright Unplugged launched a campaign to call attention to the incident, here’s the kicker: birthright learned about the woman’s plans from her mother, who — apparently out of concern for her daughter’s safety in the Mideast — forwarded them an e-mail in which her daughter details her itinerary and explains that if birthright israel learned of her plans, she would be dropped from its upcoming trip.

The spat highlights some complex questions with which birthright must contend: how to keep out those it does not see as its target audience while remaining open enough to meet its goals; and whether keeping out people like Sierra, who was seeking to explore the political issues in Israel as well as her Jewish identity, is the most effective way of furthering the program’s goals.

Since birthright’s goal is to bring as many young Jewish adults to Israel as money will allow, as few applicants as possible are turned away, officials say.

This means that some who aren’t birthright’s target audience can slip through the cracks, including non-Jews and those who have previously taken part in a peer trip to Israel. Had birthright not been contacted by this young woman’s mother, its officials say, they’d never have known of her plans.

“This is the best possible policy that we decided to endorse, bearing in mind the need to be loyal to our partners and the goals that they set for us,” said Gideon Mark, national director of marketing for the birthright israel program.

These goals, he said, include strengthening participants’ Jewish identities, their relationship with the State of Israel and Jewish solidarity worldwide.

Of Birthright Unplugged, he said: “Theirs is a tiny organization which tries to build on a very successful brand, taking part of its name, trying to teach potential participants in Taglit-birthright israel how to go to meet with Palestinians with a generous gift funded by the Jewish people. And when Taglit-birthright israel does not cooperate, then they go to the public and complain.”

But Birthright Unplugged — which says it has hosted just more than 20 young Jews on its programs since its first trip last summer, and expects to bring an additional 15 or 16 this summer — denies the charge.

“We started this program to put trip participants in conversation with Palestinian civil society, to learn firsthand about the situation in Israel/Palestine, and to use their knowledge to make positive change in the world,” said Hannah Mermelstein, co-founder of Unplugged.

“By denying Sierra the opportunity to have this educational experience, birthright israel is further proving the need for our existence.”

Birthright Unplugged takes young Jewish adults through the West Bank to “try to get people to understand what it means to live under occupation,” Mermelstein said. Some of those who’ve taken part in Unplugged have previously been on birthright israel trips, she added; others have taken part while on their year abroad in college, or while visiting Israel with their families.

The program also takes young Palestinians living in refugee camps to their ancestral homes in Israel.

The group’s name, Mermelstein acknowledged, is a reference to birthright israel, but also refers to something larger.

“We are against this concept of a Jewish birthright to this place,” said the Boston-based Mermelstein.

“We’re not afraid of people going on birthright israel, seeing what they have to say and then coming and seeing what we’re showing them on our trip,” she said. “It seems like birthright israel is afraid of having people see things that would put into question the perspective they’re trying to give their participants, or provide information that isn’t controlled by birthright israel.”

The group is funded largely by private donations from American Jews, Mermelstein said, and recently received a grant from the Sparkplug Foundation, which funds startup projects and innovations in music, education and community organizing.

Birthright israel officials say that its programs are not political, and that it employs no ideological litmus test for participants. When politics are discussed, they say, its bent has to do with individual tour guides rather than with any official birthright policy.

Other programs in Israel explore political issues with their participants. The Bronfman Youth Fellowships in Israel, for example, runs an entire “political week” as part of its five-week programs, during which participants meet with political leaders from the right and the left; Palestinians and Israelis; Arab and Jewish members of the Knesset.

“We try to have not too far right and not too far left, because it gets a little crazy and nonrepresentative,” said Rabbi Shimon Felix, the program’s executive director.

Still, Felix said, if his program were just 10 days, like birthright, rather than five weeks, “I probably would not do the politics.”

“It would be doing a disservice to the issues to squeeze that into a half day of a 10-day trip,” he said.

At least several birthright participants have gone on from the program to work with the pro-Palestinian International Solidarity Movement in the territories. Birthright did not know in advance of their plans. Although birthright participants are interviewed before they’re granted a spot, there is no uniform roster of questions, and information about post-trip plans is not always solicited, officials said.

Bronfman fellows have landed in the Palestinian territories following the program, Felix said. But as for how the program would respond if it knew in advance that a potential participant was planning to head to the territories, he said, “We would have to think long and hard about it. We don’t have a policy. I don’t think it’s ever come up.”

For her part, Sierra, the child of an African-American mother and a Jewish father, said she had planned to take part fully in both programs in hopes of learning about “a conflict with people suffering on both sides.”

“I simply want to learn about the conflict and learn about Israel,” she said in a statement passed on to JTA by Mermelstein. “I do not believe this is mutually exclusive or a reason to remove me from birthright israel’s trip. I hope that I can continue my plans to participate with Birthright Unplugged’s tour and fulfill my dream to learn about my Jewish ancestry and learn about the Israeli-Palestinian conflict.”

Birthright Unplugged has launched a campaign among its supporters to fund a new ticket so that Sierra can still fly to the Middle East this summer.