For the fourth time in its 150 years, historic Har Sinai Hebrew Congregation is on the move — journeying away from its grand old building on Bellevue Avenue in Trenton and toward its new 9.2-acre campus off Route 31 in Pennington, Hopewell Township.

In the interim, the congregation has established administrative offices in a small house on the Pennington campus, at 2411 Pennington Rd., as it stands poised to begin the renovation and reconstruction of the 12,000-square-foot, two-story office building that anchors the property.

During the transition, Har Sinai is celebrating weekly Friday-evening Shabbat services at Ahavath Israel Congregation on Lower Ferry Road in Ewing; its Sunday-school classes are meeting at the Stony Brook Elementary School in Pennington, according to Rabbi Stuart Pollack, religious leader of the 360-family Reform congregation.

Ground breaking is expected to begin in a few months on the transformation of the Pennington campus, Pollack said as he sat down recently with congregational president Marilyn Weinstein in the interim offices.

In the first step, the building on the site will be completely renovated to establish new administrative offices and a state-of-the-art, nine-classroom religious school, Weinstein said. At the same time, a 2,200-square-foot addition will be constructed at the back of the building to house a social hall, an activities center, and a chapel that will serve as a temporary sanctuary. When Har Sinai’s new home opens in time for the High Holy Days next fall, she said, it will be one of the few synagogues and the only Reform congregation in the area. Weinstein declined to discuss the cost of the overall project, which will culminate within a few years with the construction of a separate, permanent sanctuary on the campus.

The important thing for the community to know, Pollack said, is that Har Sinai is up and running in Pennington, with a full program of activities.

“I want the community to know that we’re here. We’ve established ourselves in Pennington,” he said, “and we will shortly be beginning the renovation and building of our religious school and chapel at this site.”

The congregation moved out of its Bellevue Avenue building on Dec. 29, after selling it to the Mount Bethel Church of God, a Pentecostal congregation, the rabbi said.

“The transition went very smoothly,” Pollack said, “and we’re all very proud that a synagogue can sell to a church and it can go so smoothly. We were able to make this extraordinary transition wonderfully, beautifully.

“To many of us, it was a bittersweet moment,” he added, noting that the congregation loved the Bellevue Avenue building. “In 1929, when it opened, it was the most beautiful building in Trenton,” he said. “From the day the doors opened, it was considered a landmark.

“But we hope that the same influence, the same reaching out to the community, will take place in Pennington,” he said. “We hope and pray that we will be an asset to the quality of the religious life here. This community has welcomed us beautifully.”

The congregation is grateful for the smooth transition, Weinstein said. “I also feel we want to retain the really good things we were known for on Bellevue Avenue — the warmth and values,” she said. “I’m very confident we can carry those forward to the future. Our members are very excited about this new chapter.”

“We’re going to thrive as a congregation,” Pollack said. “We feel this gives us a tremendous opportunity to grow and evolve as a spiritual congregation and a light within the community.”