He brimmed with enthusiasm. She fumbled with concern. He wanted to be a church missionary and go with her to an Indian reservation in South Dakota.

She thought, "Uh-oh." Could be a problem.

"I went to the pastor and said, 'Joshua Ederheimer wants to go on the trip,' " recalled Dorothy Forloines, 66, an elder at the Ark and Dove Presbyterian Church in Odenton, where Ederheimer's wife, Donna, is a member. "If it's going to be a problem, let me know. Tell me how you feel."

Ederheimer, 36, is Jewish.

Last month, in a brief church ceremony, Ederheimer, a D.C. police captain weaned on knishes and matzoh balls, was commissioned as a missionary, along with Forloines and Pastor Tim Stern's wife, Kelly.

Yesterday, while his wife stayed home, Ederheimer left with 35 missionaries from Baltimore-Washington area churches for a 10-day stay at the Pine Ridge Indian Reservation in South Dakota.

Local and national officials of the Presbyterian Church (U.S.A.) said it is highly unusual for a Jew to be commissioned as a missionary.

"Off the top of my head, I can't recall" this happening before, said Herbert D. Valentine, executive of the Presbytery of Baltimore, which organized the trip. "It's wonderful. This does not mean this person has to give up their religious faith or tradition."

The missionaries will run a vacation Bible school on the Indian reservation, home to about 23,000 Sioux and within the poorest county in the country. "What we do, we do in the name of Jesus Christ," Forloines said.

But Ederheimer will forgo the religious promotion. Instead, he'll drive children to the study classes and tutor them in reading and writing. Some missionaries also will help repair housing damaged in a recent tornado.

"Here I am a Jew going on a Christian missionary trip," Ederheimer said. "I'm sending a message that it really doesn't matter what religion you are. Anyone can step up to the plate and make a commitment to helping others."

Still, Ederheimer's commission as a missionary took some arranging.

Stern, the church pastor, said he first contacted a Presbyterian official in Baltimore to clear the way.

"I said, 'Guess what, I got a guy in my church . . . he's almost in my church, and he wants to go" on the mission, he said, explaining that Ederheimer is Jewish. He said the officials were receptive.

"I thought it was cool," Stern said, pointing out that the church teaches tolerance of differences, including interfaith marriages. "He's an interesting person."

Then came the ceremony.

"We mention Jesus in the commission service. How do you want me to handle this?" Ederheimer recalled the pastor asking him. "I said, 'Instead of Jesus, substitute God.' "

At a Sunday service a few weeks ago, Ederheimer stood before the communion table next to Kelly O'Hanlon Stern. The pastor asked her a few questions, including: "Will you serve the people with energy, intelligence, imagination and love, relying on God's mercy and rejoicing in God's promise through Jesus Christ our Lord for others?"

Then he turned to Ederheimer.

"I could see people were wondering what the pastor was going to say and what I was going to say," Ederheimer said. When the pastor mentioned God but left out the part about Jesus, "people just smiled."

Ederheimer, a native of Spring Valley, N.Y., a suburb of New York City, grew up attending Sabbath services at a Reform temple. In 1985, he joined the D.C. police department. The next year, he asked his hometown rabbi to conduct his wedding ceremony with Donna. His rabbi refused.

"He told me marrying a non-Jew was a 'whorish' thing to do. He told me to put off the wedding and not marry and try to meet some Jewish girls," Ederheimer said. Until then, he had occasionally attended Sabbath services in the Washington area. He stopped.

In 1987, he went ahead and married Donna, now 35. The couple have two children, 7 and 5. His wife urged him to attend church with her. About 1993, he grudgingly agreed, despite concerns that the congregants might try to "convert me."

"She wanted our kids to have a spiritual base," Ederheimer said. "The pastor, I really liked his services. Every time I go to church, I feel a little odd. I use what I call my Jesus filter. I hear what he says about God and what's right. I kind of filter out that about Jesus."

In 1994, feeling the tug of his Jewish roots, he revived Shomrim ("Guardians" in Hebrew), an organization for local and federal Jewish law enforcement officers, in the Washington area. He served as the group's president until 1997 and remains active and in touch with the organization's rabbi, Saul Koss.

"While I haven't been to temple, he has been my link to my Jewish heritage," he said.

As unusual as it is, Ederheimer appreciates the opportunity to go on the mission.

"Without joining the Peace Corps and going away for years and years," he said, "this is my baby step toward putting my money where my mouth is."

CAPTION: Joshua Ederheimer, a Jew, is now a church missionary.