From the moment Vanita Morgan knelt on her left knee at the yellow chalk line it was clear she meant business.

Cradling her marble in her right hand, she gently turned it around a few times in her fingers. With intense concentration, she prepared herself, knuckled down, gave the blue cat's-eye taw a few last turns and shot.

Two green cat's-eyes bounded out of the ring, Morgan's taw remained within, and she was on her way to becoming the D.C. girls master mibster for the second year running.

The event, the Third Annual D.C. Marbles Championship at the Randall Recreation Center, South Capitol and I streets SW, was cosponsored by the Unit Operations Division of the D.C. Department of Recreation and the TV show Big Blue Marble.

During the past few weeks, 499 children have participated in elimination tournaments in each of the city's eight wards. The four girls and 12 boys competing Saturday - the best from each ward - were vying for the city championships.

The best of the best, the boy and girl champions and runners-up, will compete in the 55th annual national championship to be held in Wildwood, N.J., the end of next month.

The two champs were Morgan, 13, of 810 K St. NE, and Abraham Wossen, 13, of 1500 Massachusetts Ave. NW, and the two runners-up, Steven Morgan (Vanita's brother), 12, and Lisa Clayton, 9, of 5338 B St. SE. The citywide events were open to youngsters aged 14 and under.

Though there are numerous marbles (mibs) games, the one played Saturday was a modified version of "ringer," the game played in the national competitions.

Thirteen marbles are placed in a cross in the center of a 10-foot ring. Players, using a larger marble called a taw, try to knock the center marbles out of the ring. A player continues shooting as long as at least one center-ring marble is knocked outside and the player's taw remains within the ring's boundaries. After the first shot, from outside the ring, the player shoots from the taw lands, until the player loses a turn.

The person to knock the most marbles out of the ring is the winner. While shooting, the player must "knuckle down" - keep at least one knuckle in contact with the ground at all times.

Wossen, shooting with marksman precision, beat Steven Morgan the best out of five games in the final match. Morgan was pleased nonetheless, and said that "it feels good" to be the number two marble in the city. He participated in last year's citywide tournament, says he did better this year and "hopes to win next year."

His sister, asked how she felt about her brother being the runner-up, jokingly replied, "I'm glad he's going along with me (to Wildwood) even though he is bad."

Of her own success, Morgan, who has been shooting marbles for a year and a half, said she felt "great." About retaining her title: "The second time: double great."

Morgan placed sixth in the national finals last year and said she thinks she will do better this year.

Wossen, even though he took home the title, wasn't sure he had the game in the bag: "I thought he (Morgan) was going to win me." But Wossen said he gained confidence by reminding himself that he "used to play in (his) country."

His country is Ethiopia, from which he and his family arrived four months ago. Except for a one-night layover in New York, Wossen says he has not seen any parts of America except D.C. Therefore, he is looking forward to going to New Jersey for the nationals. Of the nationals, he said he "might win or might lose," but he thought that he would enjoy it either way.

Lisa Clayton, holding her trophy, which to exaggerate slightly, was almost as big as she, said that she's shot marbles only "since last year." Asked how it felt to be a winner, sh grinned widely, hugged her trophy, shyly turned her eyes to the ground and in a very small voice said "fine."

Among the contestants was Bernard Roach, 13, the 1976 D.C. champ and the 1977 runner-up. Roach seemed impatient while shooting. "Take your time," they told him. But he didn't, and after disappointing shots he would stand, his lips pursed, shaking his head "no" to himself.

In the manner that must have been responsible for his winning the sportsmanship award at last year's nationals, he said, "I just lost; they're good." How did he feel about not going to the nationals for the first in three years? "I'm not upset: it ain't nothing but a game."

Wossen came over to Roach and asked, "What happened to you?"

"My fingers were sweating, man."

The International Telephone and Telegraph Corporation, sponsor of the national championships for the past five years, will pay all expenses for the four D.C. winners to spend a week in Wildwood next month while competing in the nationals. The boy and girl winners of the nationals each will receive a $500 IT&T college scholarship.

Though the national marbles championships have been going on for 55 years, D.C. has only sent contestants since 1976. Citywide championships have been taking since 1935.

Other contestants Saturday were: Jared Brennen, 10, of 1209 34th St. Nw; Ruth Evans, 13, of 206 K St. SW; Henry Frazier, 10, of 240 W St. NW; Michael Gillis, 9, of 9th St. NW; Alisa Gorham, 14, of 1513 Bruce Place SE; Wyatt Green, 10, of 203 N. St. SW; David Griffen, 9, of 860 7th Ave. SW; James Hall, 10, of 5725 13th St. NW; Theodore Howard, 9, of 12th and L Streets NW; Samuel Oliphant, 9, of 3817 J St. NE; Bernard Roach, 13, of 182 Jolliets St. SW, and Robert Tiller, 14, of 900 Madison St. NW.