The doors of the former YMCA building on 12th Street NW were not supposed to open until 6:30 p.m. Monday, but Erica Shorter arrived an hour early, joining a line that soon stretched half a block to T Street.

Once she got inside, she rushed to a small table in the corner of the light-green gymnasium. Grabbing a pen, she signed up her two children for the St. Francis de Sales School on Rhode Island Avenue NE.

Shorter, 33, could not have afforded the Catholic school's tuition in the past. But her children were among 1,249 low-income students selected last week to receive the District's first tax-funded private-school vouchers, and she wanted them to be first on the school's list.

The public schools in Southeast Washington that her children have attended have low scores and limited programs, she said, "and I want them to be able to get all kinds of learning."

Shorter and the families of more than 500 other voucher recipients jammed into the small building, now called the Thurgood Marshall Center Trust, Monday evening and yesterday afternoon to visit tables staffed by representatives of 44 private D.C. schools that have agreed to participate in the program.

She and the other parents soon learned that arriving early did not boost their children's chances of getting into any particular school. The voucher holders still need to submit formal applications to the schools that interest them, and the schools will determine which students qualify for admission after reviewing their records.

But the line to get into the school fair was an indication of the excitement among the families who will be pioneers in the school-choice initiative, which Congress approved in January.

Ruth Martin, 68, was there yesterday with three grandchildren who have won vouchers to switch out of their public schools. She asked questions and collected information packets at several tables, saying later that she was most impressed with the Preparatory School of D.C. in Northwest. "I am looking for a place where the class sizes are smaller and they give more attention to each child's studies," she said.

The vouchers are worth up to $7,500 per child. Of the students who won grants for this fall, 1,049 attend public school or are about to start kindergarten, and those entering a grade in which the program had more applicants than slots were selected through a lottery. The remaining 200 voucher winners already are enrolled in private school but met the income guidelines for the federal assistance; they also were picked by lottery.

Sally Sachar, president and chief executive of the nonprofit Washington Scholarship Fund, which was selected to run the voucher program, said "we are absolutely thrilled" with the results of the two-day fair.

But she emphasized that the fair was just a first step in the process of matching applicants from the public school system with their new private schools. Applications to the schools are due July 9. After the schools have determined which students meet their admissions criteria, another lottery will be used in cases where a school has more qualified applicants than spaces.

Archdiocese of Washington schools, which account for almost half of the schools participating in the program, were particularly active at the fair. A large city map mounted on a stand in the middle of the gym floor showed the Catholic schools' location, and their information packets emphasized that all kinds of students were welcome.

A handout from St. Francis de Sales noted that "70 percent of our students and 40 percent of our faculty are non-Catholic."

A teacher at the St. Thomas More School, answering a question from a non-Catholic mother, said, "We don't force our religion on anyone, but we do want the kids to know the basic stuff."

Patricia A. Weitzel-O'Neill, school superintendent for the archdiocese, was at the fair both days, talking to parents and praising the school staffers who had volunteered for the tables. "This is the time of year when they are all supposed to be on vacation," she said. Lillette Green-Campbell, founder and principal of the nonsectarian Bridges Academy on Georgia Avenue NW, gave parents a thick folder that included favorable newspaper clippings going back 20 years. "We have been doing this a long time," she said.

Fifty schools are participating in the program, and some schools with very few openings decided not to attend the fair, Sachar said. She said all the schools will give parents opportunities this summer to visit their campuses. Ten parents who stopped at the table of Rock Creek International on Monday night turned up at the school the next morning for a tour, she said.

Materials distributed by the scholarship fund warned that parents might not get their first choice and urged them to apply to as many schools as possible. "Three, four or five schools is not too many!!!!," one of its guides said.

Shorter put her children's names on the informal sign-up sheet at both St. Francis de Sales and Our Lady of Perpetual Help, a Catholic School on V Street SE.

She noted that St. Francis de Sales is near Children's Hospital, where she works as a clinical receptionist, and that Our Lady of Perpetual Help is near her home.

But in the noise and confusion of the fair, some of the information she thought she heard was not correct. After visiting the St. Francis de Sales table, Shorter said she was particularly excited about the school because it had classes in several foreign languages. St. Francis Principal Matt Johnson, however, said he had only one such class, an introductory course for eighth-graders in Spanish.

Once she had time to read the scholarship fund's materials, Shorter realized that she had much more to do. She would need to complete an application form and provide her children's last report cards, test scores, birth certificates, Social Security numbers and immunization records.

All that, Shorter said, is fine with her. "It is such a great opportunity," she said.

Francesca Keys, 5, checks out the prospects for the private school she might attend in the fall with one of the District's 1,249 vouchers. Angela Sanders-McKinnis and daughters Aizley, 4, left, and Aniya, 6, talk with Holy Name School Assistant Principal Monica Evans and Principal Patricia Ralph.