At 7 p.m. the classrooms on the third floor of Mackin High School are filled with students chattering in Spanish or finishing up assignments.

The evening hour is unusual for classes at the school and the students are unusual, too. They are adults who speak little English but who are eager to learn.

"I am sleepy and tired from standing all day," said Anna Perdomo, 22, who recently arrived in this country from El Salvador.

She works as a hairdresser during the day and has a young son. "But I want to learn to speak English very well," she said.

Perdomo is one of 650 adults who learn English each year through a program run by the Spanish Education Development Center and the Spanish Catholic Center, two local organizations that have sprung up in recent years to meet the needs of the city's growing immigrant population.

"They're tired," said Michael Ellis, one of about half a dozen teachers who work this second job for a minimum amount of pay. He explained that most of the students work 10 or 12 hours a day as domestics, janitors and cooks before coming to class.

"But English can mean the difference between a job that pays $100 a week working as a housekeeper for a Latin family and a job that pays $150 a week with an American family," Ellis said.

"These people that come here are really impressive," said Mike Franklin, a teacher of an advanced English class. "They all hope so much of and in this country," he said.

The exact number of Hispanics living in Washington is unknown, but estimates range from 60,000 to 80,000, or roughly 10 percent of the District's population of 623,000.

The 1980 census counted 17,652 Hispanics in the District but city officials and members of the Hispanic community agree that the actual number is probably closer to 60,000 to 80,000.

The numbers have been swollen in recent years by refugees escaping the civil wars in Central America.

The English classes held at Mackin, a Catholic boys' high school at 2200 California St. NW, cost $25 for 10 weeks or $30 to $35 for five weeks.

The Spanish Education Development Center was founded in 1971 by a group of immigrant parents. It began as a small day-care program in a church basement. Now it is housed in a three-story building at 1840 Kalorama Rd. NW and offers a variety of programs to help Hispanic children, youths and adults succeed in their adopted country.

However, "the idea is not just for them to adapt," explained Maria del Rosario Basterra, director of the preschool.

"We also want to provide them with a sense of cultural identity, to be proud of their country," she said.

Brother John Blaszczak of the Spanish Catholic Center, who with a SED Center staff member codirects the English classes, emphasized that the classes are an important gathering place where Hispanic culture prevails. "My goal is to hold up their culture as something to be valued," he said.

During the morning hours, the center's first floor and basement house 60 children from 2 to 5 years old.

Their favorite part of the day is spent grouped in a circle around a teacher with a guitar. About half of the songs are sung in English and the rest in Spanish.

Like the singing sessions, everything at the SED Center day-care program is done in both Spanish and English. It is the only preschool and day-care center in the District where children are taught to read, write and speak in both Spanish and English, Del Rosario Basterra said.

"The idea is that when they leave the center they will be able to read in both English and Spanish and be more able to succeed in the public schools," she said.