* Orthodox delegation expected at Mass but did not come
* Crowd at service one of smallest ever for Francis
* Pope leaves for Azerbaijan on Sunday (Updates with pope meeting patriarch, quotes on conversion)
By Philip Pullella and Margarita Antidze
TBILISI, Oct 1 (Reuters) - Pope Francis on Saturday said Mass for an unusually small crowd of just a few thousand Catholics in Georgia, a celebration that was further dampened when a delegation from the Orthodox Church stayed away.
Ex-Soviet Georgia is overwhelmingly Orthodox Christian and less than 1 percent of the population is Catholic, according to government figures.
Still, organisers had been hoping for a much bigger turnout than the some 3,000 people who came to the Mass at a stadium in the capital that has a capacity of 25,000.
It was one of the smallest crowds ever seen at an outdoor papal Mass on Francis' 16 foreign trips so far.
In another setback, a delegation representing the Patriarch of the Georgian Orthodox Church, Ilia II, that the Vatican had expected to come to the worship service, did not show up.
The Georgian Orthodox Church is one of the more conservative in the worldwide Orthodox community and has an extreme right wing that is totally opposed to any dialogue aimed at reunion with the 1.2 billion member Catholic Church.
The Orthodox Church, which now numbers about 250 million adherents, split with Rome in the 1054 schism that divided Christianity into eastern and western branches.
A small group of right-wing Georgian members have dogged the pope at every stop to protest against the visit, carrying signs reading: "Vatican is a spiritual aggressor" and "Pope, arch-heretic, you are not welcome in Orthodox Georgia."
In an apparent effort to allay their fears, Francis told a meeting of priests and nuns that they should not feel like they had a mission to convert Orthodox worshippers, saying this would be "a great sin".
"Never try to practice proselytism against the Orthodox (church). They are our brothers and sisters," he said.
Despite the theological differences between the two Churches, Francis had three cordial meetings with the ailing, 83 year-old Patriarch Ilia.
At the last event in Georgia, he went to the riverside town of Mtskheta, 20 km (12.5 miles) from Tbilisi, to meet Ilia in the 11th-century Svetitskhoveli cathedral, the seat of the Georgian Orthodox Church.
There, Ilia expressed his "deep esteem and fraternal love" for the pope.
Under Francis, who was elected in 2013, the Vatican has made a concerted effort to improve relations with Orthodox Christians in the hopes of an eventual reunion.
Earlier this year, he held a historic meeting with Kirill, the patriarch of the Kremlin-back Russian Orthodox Church, the largest and most influential in world Orthodoxy.
Francis leaves on Sunday for a day-long stop in overwhelmingly Muslim Azerbaijan before returning to Rome. (Editing by Richard Balmforth)