WASHINGTON — Lila Faria, 19, a student at New York University, heard the whine of a bomb siren for the first time last month in Jerusalem. Along with several dozen other Americans on a trip with the Taglit-Birthright Israel organization, she was quickly hustled into a bomb shelter.

“There was a feeling of uneasiness among the group because it made the situation less exciting and a little more realistic,” Ms. Faria said in an interview from her home in Maplewood, N.J., a few days after she returned. “We suddenly realized that yes, there were bombs being fired, and people could be seriously hurt.”

The conflict between Israel and Hamas did not stop Ms. Faria and more than 6,000 other participants in Birthright from traveling to Israel in the past month, Birthright officials say, but some 3,000 out of an anticipated 31,000 participants have canceled their trips with the program this season, which runs from May to September. The nonprofit organization pays for 10-day educational trips to Israel for young Jews, the vast majority from the United States.

The drop in participation since the violence started in Israel and Gaza is consistent with other times of violence in the Middle East, said Gail Hyman, a Birthright spokeswoman. Since the program began in 1999, no trip has been canceled because of security concerns.