"We have unity in the essentials of faith and diversity in the nonessentials," the Rev. John S. Danilak said in describing the relationship between the Eastern and Western traditions of the Catholic Church. Both traditions have their authority in Rome.

"The essentials are faith, tradition and the Bible; the diversity is in the culture, customs and the language" that have created the two basic traditions as they developed separate, one in Byzantium, the other in Rome.

Danilak is pastor of the recently constructed St. Gregory of Nyssa Church in Beltsville, a Catholic Church of the Eastern - in this case, Byzantine tradition or rite - instead of the Western or Latin rite followed by the majority of Catholics in the United States.

Citing the three-bar or Greek cross marking the church buildings, and the icon screens before the sanctuparies, Danilak said, "If you went to a Greek Orthodox Church and then to St. Gregory, you probably wouldn't notice the difference." He pointed out that the liturgy and language of his church is identical to those of the Greek Orthodox, except for a papal litany or prayer for Pope Paul VI.

Though William Cardinal Baum of the Archdiocese of Washington will preside over a divine liturgy this Sunday at St. Gregory following the 3:45 p.m. dedication of the new building at 12420 Old Gunpowder Rd., Baum has no ecclesiastical authority there.

The Most Rev. Michael J. Dudick, DD., Bishop of the Byzantine Diocese of Passaic, NJ, is the prelate with authority over St. Gregory, and will celebrate the actual dedication. The archdiocesan jurisdiction for the Byzantine Ruthenian Church in this country is in Pittsburgh. It is called the Archdiocese of Munhall, after a section of the city popular with Slavic migrants. St. Gregory first started in Washington at St. Patrick's Academy in 1956.

Msgr. Walter Paska, a member of the Byzantine Ukrainian Church, another Eastern rite church with a separate hierarchy falling under papal jurisdiction, recounted the history of the Byzantine Catholics in the United States.

"The Ukrainian and Ruthenian Catholic began arriving in Pennsylvania around 1875 to be coal miners in the anthracite region," he explained. "They were from the Austro-Hungarian empire. Those who came from north of the Carpathian Alps were called Ukrainians and those from south of the mountains were Ruthenians. They had their first church in Shenandoah, Pa., in 1884."

The first bishop was named in 1907. Later, the two groups formed separate hierarchies. Today there are about 300,000 worshippers in each church, he said.

Holy Family Parish, at 16th and Blagden streets NW, is the Byzantine-Ukrainian Catholic Church in this area. The other three Eastern rite Catholic churches in this area are:

Epiphany of Our Lord, 3410 Woodburn Rd., Annandale, a sister church to St. Gregory.

Holy Transfiguration Melkite Church, 9201 Leesburg Pike, Vienna, which recites part of the liturgy in Arabic.

Our Lady of Lebanon, 7164 Alaska Ave. NW, in the Antiochian Maronite tradition of the Eastern rite.

"There were abuses in the past, but Rome has been very meticulous about not interfering with our separate national traditions for about 100 years," said Msgr. Seely Beggiani, pastor of Our Lady of Lebanon and rector of the adjoining Maronite Seminary.

"Though they are often quite different, the priests, the sacraments and the liturgy of the Orthodox Church are valid in the eyes of the Catholic Church," Beggiani said.

The National Shrine of the Immaculate Conception has an elaborate Byzantine chapel, with gold mosaics and colorful icons.