The Christmas tree is up and lit at Christ Lutheran Church in Marietta, Ga., and the Rev. Rusty Edwards just can't wait to sing a few lines of "O Little Town of Bethlehem," his favorite Christmas song.

" 'The hopes and fears of all the years are met in thee tonight,' " Edwards said, recalling the 1867 lyrics by Phillips Brooks. "It's the greatest line of any hymn ever written."

But the liturgical calendar, which lays out the songs and Scriptures for each Sunday of the church year, doesn't include those beloved Christmas carols and hymns until Dec. 25. That's because, despite what Macy's and Wal-Mart might say, Christmas doesn't start until Dec. 25 and in many churches runs past New Year's Day.

So, during the four Sundays of Advent, Edwards's church will sing Advent hymns, not Christmas ones. It's an area of church music that many musicians say is overlooked and underdeveloped, although a new burst of Advent hymnwriting is helping to fill the gap.

For Edwards, the anticipation of those favorite carols is like a 5-year-old waiting for a visit from Santa on Christmas Eve. Desperate for some Christmas music, the congregation held a carols service on a recent Saturday night. Sunday morning caroling would have to wait a few more weeks.

In Catholic and many mainline Protestant congregations, the church year is partitioned into seasons. Unlike a secular calendar, the liturgical church year starts the first Sunday of Advent, which is four weeks before Christmas. This year, Advent started Nov. 27.

The "season" of Christmas doesn't actually start until Dec. 25 and usually lasts 12 days -- with those eight maids a-milking and seven swans a-swimming -- until the Feast of the Epiphany, Jan. 6.

That gives churches two Sundays, Dec. 25 and Jan. 1, to sing Christmas carols and songs this year. Edwards, for one, says he understands the rules but still wishes he could sing more of the songs he's already hearing on the radio.

"When we send missionaries to other countries, we tell them to get in tune with the culture and try to relate to them," Edwards said. "But we don't do that with our culture."

Advent's true believers say the ancient tradition is a season of preparation and anticipation, a sort of kinder and gentler version of Lent, the 40 days of prayer and penance leading up to Easter.

Advent has its own songs and traditions -- including lighting the four candles of the Advent wreath -- and musicians say it would be premature to sing Christmas songs about the birth of Christ before he's actually born.

"It would be a little bit like opening your Christmas presents before Christmas morning, like sneaking into the closet and ruining the surprise," said Kathleen Pluth, a Catholic hymnwriter in Washington. "It's a bit of a letdown."

Michael McCarthy, the music director at Washington National Cathedral, said, "Would you sing 'Happy Birthday' before someone's birthday? That's basically it."

So what's wrong with a little Advent music? To start, there's not much of it -- at least much that is as familiar as Christmas carols. The perennial favorite is "O Come, O Come, Emmanuel," based on an ancient 12th century chant. Others include "Come, Thou Long Expected Jesus" and "Comfort, Comfort Ye My People."

Pluth, who has written hymns for Advent, says that " 'O Come, O Come, Emmanuel,' yes, is overdone." Edwards, too, has written Advent hymns, including one, "To a Maid Engaged to Joseph," that can be found in Methodist and Presbyterian hymnals. Pluth is especially proud of her Advent hymn, "On Walls Around Jerusalem."

Mary L. VanDyke, director of the Dictionary of American Hymnology Project at Oberlin College in Ohio, said hymnwriters are slowly rediscovering Advent, which she said has been overshadowed by all the "bright tinselly stuff" of Christmas.

"People are just so anxious to sing Christmas carols that they're smothering the Advent hymns," VanDyke said. "But there's a lot of new activity going on in composing Advent hymns. These aren't old, yellowed hymns."

Pluth and others say Advent hymns are actually easier to write than Christmas songs, in part because the sweet sentiment of Christmas has already been captured for the ages. Advent hymns should have a sense of longing, expectation and waiting.

And, said Peter Latona, director of music at the Basilica of the National Shrine of the Immaculate Conception in the District, the type of Advent music that gives him "goosebumps" should also look with hope to the end of time.

"That's what all the good Advent texts have in them -- the second coming and the role of Jesus as savior, not just the baby in the crib," he said.

The Rev. Rusty Edwards, right, a hymnwriter, would like to sing more Christmas carols at Sunday services during Advent, but the liturgical calendar says the season of Christmas begins Dec. 25.