At 2 o'clock yesterday afternoon, in the Courtyard Cafe of the Sheraton Washington Hotel, a man in a blue blazer reached under his chair and pulled out a cassette from a briefcase. He put it on a small silver machine. "You like to hear my music?" Manuel Roman Marzan asked. Suddenly the room wafted with good old gospel -- not North Americano gospel, but sassy, jazzy Latino gospel, like something a spritzed-out, saved-again Desi Arnaz might croon, full of salsa and horns. You couldn't help but like it.

Patrons kept eating. Music kept wafting. Manuel Roman Marzan of Puerto Rico was on the front porch of religious bliss. The tune his machine sang would doubtless suffer from the best of translations, but roughly it told the story of a conversion. Afterward Manuel said with piercing ardor: "I was reborn in 1966. It was in my house. My mother was praying for me. It was a miracle. My object now is not to get famous, my object is to tell the people there is a hope in Jesus."

Pause. "I wouldn't mind being a little famous."

Manuel Roman Marzan is one of thousands of electric preachers and performers and video hardware salesmen who came to town this weekend for the start of the 39th annual convention of the National Religious Broadcasters. Like any convention this one rode in on hope and blizzards of paper.

The famous names of the Wired Kingdom -- like Rex Humbard and Billy Graham and Jim Bakker and Pat Robertson -- were not on view yesterday. Celebrities generally arrive late. It is thought everyone will be in place by today, or at least tomorrow. Before the convention is over evangelist Ronald Reagan has been invited to witness a gospel of one sort or another.

What you mostly ran into yesterday, as a convention struggled to life, as believers of the electronic church hammered and plugged and shag-carpeted their exhibits into place, were the lesser known, but no less fevered, spreaders of the electric Word.

Like the folks at KMJC, 910 on your radio dial, 5,000 watts of 24-hour prayer power for the greater San Diego area. KMJC used to be "Magic 91," big California rock. That was before Dr. James C. Gates got hold of it. Nowadays KMJC stands for "King and Master, Jesus Christ." Awhile ago Dr. Gates used to have station KLRO. They marketed that one as "Tune Into the Good Life."

"Would you like some candy?" Mrs. Gates said yesterday as she stood at her husband's rising booth. (There were a few pamphlets, a lonely banner suspended from a curtain.) Before you could say no thank you, there was a little cellophane of hardtack, tied with a ribbon, in your mitt. "Give them to a friend," she said brightly.

A few feet away Jim Bakker's lavish exhibit was going up like a shepherd's tent. It featured a gigantic living room set, with crushed baby blue settees and wing chairs and gold-trunk coffee tables, adorned with Bibles and vases of paper flowers. The PTL club, as anybody knows who has not been sick or in Europe, satellite-beams to millions from its home base in Charlotte. It stars the Reverend Jim and his wife Tammy.

Bishop Jose A. Reyes, of the Church of God of Prophecy, is attending the convention, which runs through Wednesday. Bishop Reyes was resplendent yesterday in a glossy black suit and silvery hair. Bishop Reyes lives and works in Cleveland, Tenn., from which far-flung point he beams the word to listeners throughout Latin America. It may sound a bit odd for a little town up from Chattanooga to be the source of a thriving Hispanic electronic ministry. But stranger things have occurred. Cleveland, Tenn., is where the Church of God of Prophecy got its start, back in 1903. Now they've got a publishing house, a university, and a three-story church, says the bishop. The address on the bishop's card is Bible Place. "Our movement started on a mountain. At that time Cleveland was considered a big town. They moved the church from the mountain to the town."

Youth With a Mission, from Tyler, Tex., is also here. Yesterday the chief mission seemed to be getting the exhibit up. A burnt-orange sofa had been moved in, along with an end table and a lamp. A man in a cowboy shirt and boots and Western-cut jeans brought out a Personal Prayer Diary ($14.95, leatherette binding) for which orders happily will be taken. The Personal Prayer Diary gives you something every day of 1982. The heart of it is "the daily walk." Youth With a Mission is in 40 nations and has about 3,000 committed young missionaries. They even have an 11-ton ship.

George Gallup has reported that half of all American adults may occasionally be tuning into the quicksilver image of the Lord on the magic box. If there is a new Jerusalem that is nigh, its name may be video. However, other surveys, notably from Arbitron and Nielsen, say the religious audience is far lower than is claimed. One researcher says that religious radio is reaching less than 2 percent of a nationwide audience. "It's a little like cost accounting: your costs are what you say they are," said an NRB spokesman.

At last night's formal opening, black gospel singers taught the audience how to lean on Jesus. "If you confess the Lord/ Call him up," they sang. However, the audience wasn't quite in a revivalist mood. Maybe it will come later.

Then a preacher from the Mount Zion Missionary Baptist Church in Watts got up. His name is E.V. Hill, and Time magazine named him a while ago one of the seven most effective preachers in America. First the preacher told a joke. It was only slightly off color. It concerned a mule, and somebody who was made to kiss it. "I think it will be acceptable," he said. "I got it from Billy Graham and tried to clean it up a little bit."