Instead of the Dalai Lama, the 2006 International Prayer for Peace conference will have two Chinese representatives, Bishop Peter Feng of the Hengshui diocese in Hebei province and an accompanying priest. Although both are from China's state-approved church, which the Vatican does not recognize as Roman Catholic, Bishop Feng's 2004 consecration was approved by the Holy See.

But it was the Dalai Lama who was featured in an iconic photo with Pope John Paul II, who summoned 30 world religious leaders for the original peace conference to the picturesque Italian city of Assisi on Oct. 27, 1986, during the waning days of the Cold War. The photo of the pontiff standing next to the Dalai Lama, with both men holding potted plants, made its way around the world.

Georgetown University will mark the 20th anniversary of this conference starting at 5 p.m. tomorrow, when 120 religious leaders will gather. The opening ceremony will feature Cardinal Theodore E. McCarrick, Catholic archbishop of Washington; Georgetown University President John DeGioia; and Andrea Riccardi, founder of the Catholic lay movement Community of Sant'Egidio.

The Dalai Lama, 70, was omitted from this year's guest list because of health problems, not political reasons, said Claudio Betti, spokesman for the Sant'Egidio community, which is organizing the gathering.

"He is one of the most difficult people to get," Mr. Betti said. "You would have had a lot of problems with China [if he came], but that is not the real reason" for the Buddhist leader's not being included on the guest list. "He was not invited because he is not well."

However, Kate Saunders, spokeswoman for the International Campaign for Tibet, said the Dalai Lama was at the Mayo Clinic in Rochester, Minn., last week for a routine medical checkup and is in "extremely good health."

"The Dalai Lama is recognized as one of the leading voices for peace and interfaith dialogue worldwide," she said. "If he has not been invited, it is likely that pressure from the Chinese authorities may have been involved, as we have seen on numerous occasions.

"Chinese officials would be unstinting in their efforts to control the agenda and prevent any possible reflection on the lack of genuine religious freedom in China today."

A call to the Chinese Embassy's press office was not immediately returned.

The only Buddhist representative at the gathering is a Zen Buddhist leader from Japan. There are numerous Catholic, Orthodox, Jewish, Muslim and Protestant speakers with a sprinkling of other religions. Mr. Betti said the conference, held every year since Assisi in European venues and at Georgetown for the first time in the Americas, was reconfigured to be completely in English and include many American religious figures.

"In order to impact the society here, we needed to make it more American," he said. "America is a universe all its own. Look how many high-level American Muslims you have at this conference."

On Thursday, the event will split into three panel discussions held at five venues around campus. It will close Thursday afternoon with a service for peace at Holy Trinity Catholic Church at 36th and N streets Northwest in the District, and then a "peace procession" from the church to a closing candlelight ceremony involving 3,000 people will be held on Healy Lawn at the main campus.

The conference "is very important this year because it's in Washington," Mr. Betti said. "At this moment, dialogue doesn't seem too popular anymore."