In most cities, anyone with the sudacity to claim he has found the true path to Heaven is likely to get an argument.

But here is Washington, there is unanimity on this touchy question. Catholics, Buddhists, Hanafi Muslims Jews, Orthodox Serbians, "Moonies" Swedenborgians and Spiritualists can all agree - to find Heaven, head for 16th Street.

From the White House to the Maryland line, 16th Street plays host to virtually every imaginable religious and quasireligious sect. Big churches and small, Eastern and Western, orthodox and unorthodox - 45 of them altogether, by the latest count - coexist on this broad and stately street, sometimes two and three to a block.

At 16th and Jonquil streets, two synagogues gaze across at the headquarters of the Hanafi Muslims, some of whom laid siege in March 1977 to the B'nai B'rith near 16th Street and Rhode Island Avenue, holding scores of terrified hostages for a tense day-and-a- half.

But there have been only a few incidents of name-calling - and nothing worse - between the Jews and Muslims who practice their faiths and tend their equally immaculate grounds on this placid, tree-lined stretch of 16th Street.

At 16th and Harvard streets, on the other hand, would-be worshipers are frequently confused by the proximity of All Souls Unitarian Church on the east side of the street to the Unification Church of the Rev. Sun Myung Moon on the West side.

All souls, long known for its "open pulpit" and its hospitality to antiwar demonstrators, Black Panthers, homosexual activists and other nonconforming groups, recently offered a sermon entitled, "The Unification Church - Far Out, But Right Across the Street."

But perhaps the most incongruous church on all of 16th Street is the 19th Street Baptist Church, located at 16th and Crittenden streets, Read on - that was not a typographical error. The 19th Street Baptist Church, whose pastor is the Rev. Jerry A. Moore, the lone Republican member of the D.C. City Council, used to be on 19th Street, as you might expect, until it took over a synagogue building at its present address in 1975.

"We didn't want to change the name, because the 19th Street Baptist Church was very historical," explains church archivist Naomi Rushig.

Another factor militating against a name change was probably the fact that the name "16th Street Baptist church" had already been staked out. It stands at 16th and Nicholson streets NW.

St. Luke's Serbian Orthodox Church, at 5917 16th St., is the product of a bitter schism.Five years ago, a group of parishioners at the St. Luke's Serbian Orthodox Church in suburban McLean angrily left their church to found the St. Luke's on 16th Streets, and both sides are still claiming to be the rightful voice of Serbian Orthodoxy in the Washington area.

At the heart of the dispute was whether the patriarch in Yugoslavia had the authority to order a major reorganization of the American branch of the church. The majority of the McLean congregation said no, in effect declaring their religious independence from the mother country. But a minority said yes and moved to 16th Street.

Despite 15 years of litigation on this and related issues, and despite a 1976 Supreme Court ruling generally upholding the patriarch's power, the matter seems no more settled than ever.

There have been mergers - as well as fissures - in the history of Church Row, as the street has been called. In 1974 the Hamline Methodist Church, a predominantly white congregation at 16th and Allison streets, had a declining membership and a large, evermore-expensive church building.

Hamline Methodist might have closed or moved out to the suburbs, as other churches in similar straits have done. Instead it combined with Simpson Methodist, at 13th and Monroe streets NW - which had a small deteriorating building and a growing, largely black congregation - to become the Simpson-Hamline United Methodist Church. "It really made a wonderful merger," says one long-time parishioner.

But even when churches do leave 16th Street, they frequently pass their facilities on to other faiths. So religion itself is rarely the loser.

The Mormons closed their temple at 16th Street and Columbia Road because, a spokesman explains, the building was badly run down and its parishioners were gradually moving out toward the suburbs. After an abortive effort to establish a recording studio there, the building reverted to its original use last year. That is when the Unification Chruch (whose members would rather not be known as "Moonies" but as "people who have blood in their veins," according to the Rev. David Hose) bought the property and promptly hoisted its gold-painted aluminum symbol of the 12 human personalities and the 12 ways to the Kingdom of God high above the entrance.

At about the same time, the Unification Church decided to vacate a house occupied by some of its faithful at 16th and Varnum streets, making way for the tiny Temple of Cosmic Religion, a Hindu-oriented sect whose typical Sunday service attracts a throng of anywhere from five to 10 dedicated followers.

The Church Universal and Triumphant Teaching Center, at 16th and Decatur streets, occupies a commodious white mansion that used to be the Honduran Embassy. There is no sign outside the center, which has been there for three year. "We haven't gotten around to it," explains the Rev. Sigrid Carlson, an enthusiastic woman with a ready smile.

The sect was founded in 1958 by Mark L. Prophet - "and that by the way, was his real name," says Carlson. When Mark Prophet died in 1972 she adds, he became the Ascended Master Lanello, joining Jesus, Buddha, Confucius, Mohammed, Pope John XXIII and St. Germain in the church's "great white brotherhood".

Like the Temple of Cosmic Religion and many of the smaller faiths on 16th Street, the Church Universal and Triumphant recognizes the soundness of most of the world's established religions. "We pull out the truth from East and West as it comes from the ascended masters of East and West," says Carlson, adding, "Religion and science are the same thing because energy and God are the same thing."

Since Mark Prophet's death, the leader of the church - which is headquartered on 218 acres near Malibu, Calif. - has been his widow, Elizabeth Clare Prophet, now "the messenger for the great white brotherhood," says Carlson. "She is really the most tremendous person I have met in my life."

Among other recent events, the church held a seminar on the precepts of the book "Jonathan Livingston Seagull," which has "many wonderful principles in it and great truth," says Carlson.

The National Spiritual Science Center, at 5605 16th St. NW, is a "non-denominational" center for the study of metaphysics, clairvoyance and general "spiritual development," according to the Rev. Diane S. Nagorka, who runs it.

"We're not spiritualists," Nagorka insists. "What we do is more work. W do it wide awake. There's no hocus pocus."

The center does double duty as Nagorka's home, which she shares with her husband, a former U.S. Information Service cultural attache. Downstairs, where the Sunday night healing services are held - "magnetic healing . . . the laying on of hands," Nagorka explains - the rooms are dimly lit and abound with exotic looking spiritual-science paraphernalia.

The healing is a great success, says Nagorka. "We have seen dumbness disappear, we have seen all kinds of nervous ailments disappear," she says. "We have had bones mended. It's just across-the-board success with the healing."

Duffy Farrand tries to avoid discussing religious matters when he teaches his classes in radio and television communications at George Washington University. But when he gives student his home phone number, he feels obliged to warn them not to hang up just because the voice on the end of the line answers, "Temple of Cosmic Religion."

At GW, Farrand, a former producer of children's shows for WTOP-TV (now WDVM), lectures in a jacket and tie like most of his colleagues.At home, he trades his secular clothes for a white robe and bare feet, and becomes Nama Deva, the Temple of Cosmic Religion's local head priest.

Farrand is one of five Cosmic Religion adherents who live as well as worship at the temple, a converted town house at 16th and Varnum streets NW. "We're basically a Hindu-oriented nonsectarian religious group," explains Farrand. "Most of us, I guess, felt religion was like a Chinese dinner. We grew up on religion and we wanted more."

The temple holds services every day, open to nonresidents, and on Sunday there is a ritual in Sanskrit that has stayed essentially the same for a thousand years, according to Farrand. In the temple rom itself, portraits of Jesus and Buddha hang alongside that of Panduranga, the 10th and final incarnation of the Hindu God Vishnu, who is shown standing in a seemingly endless sea of children.

Panduranga is a messiah who has yet to make an appearance on Earth, Farrand explains. "I'm waiting myself," he says.

The temple's followers are vegetarins, and neither smoking nor drinking is allowed on the premises. "But we're pretty laid back here," says Farrand. "Most of us have a pretty good sense of humor . . . We don't claim to have anything new in the line of truth that hasn't been around for thousands of years."

No one seems entirely sure just why 16th Street has attracted all this churchly activity. "Because they built them," says the Rev. David H. Eaton, senior minister of All Souls, with a grin.

Among possible less frivolous explanations:

Sixteenth Street is a major hus and commuter route easily reached from all corners of the Washington area.

Large and lavish mansions and embassies were built there around the turn of the century when Mrs. John B. Henderson - a wealthy hostess who "ruled Capitol Hill with an iron hand and a capricious mind," according to one local historian - waged a determined campaign to make the street fashionable (with mixed results). Most recently, some of these colossal building have lost their original tenants and been converted into, among other things, churches.

D.C. zoning laws bar virtually all commercial enterprises from one end of 16th Street to the other.

Finally, the older, established churches seem to have attracted newer, unestablished ones in quest. of large and stable congregations, and that extra undefinable something that seems tocome with a 16th Street address.