One of the District's summer youth employers has withdrawn abruptly from the program, forcing the city to reassign about 800 teen-agers to other summer job training programs, according to city officials.

After the firm, the American Institute for Transportation and Business Development, withdrew, many of the youths were transferred to programs run by the city's largest summer jobs contractor, Associates for Renewal in Education, which also has been plagued by problems. The company's shaky finances have prompted city officials to develop contingency plans in case that firm fails.

Daryl Hardy, branch chief for the District's $16.5 million summer jobs program, said the American Institute firm "opted out" of the program last Friday after meeting with city officials about problems with the training. "We had to scramble" to place the youths in other programs, he said.

City jobs officials said this week that the firm didn't have an official contract with the city, but agreed to train 800 to 1,000 youths in exchange for their work on the firm's projects. It could not be determined yesterday if the firm received any money from the District.

Brenda Hamer, the firm's executive director, could not be reached for comment.

The firm started the program June 30, after subleasing two floors in a building occupied by Strayer College at 1100 Vermont Ave. Hardy said the youths were getting experience by copying the firm's records onto index cards.

Scottie Borders, a former firm employe who is now a mortgage banker in Alexandria, said he visited the job site on July 14 and found "kids crowded into rooms, relaxing with their feet up on the table and throwing paper."

Charles Palmer Jr., director of Strayer College, said the college got no notice that the firm, which has not paid its rent, was moving out, nor were officials told how large the program was.

"We had been told there would be 150 participants, and we were a bit surprised by the number of people," said Palmer. He said the classrooms were disheveled and littered with paper when the firm moved out.

Associates for Renewal in Education, the firm that will employ the reassigned youths, owes $240,000 to the Internal Revenue Service and $27,700 to the D.C. Department of Employment Services, which has awarded a contract to the firm every summer for six years, according to records. The firm also owes the city about $160,000 in back rent for its offices, which are located in the former Edmonds School, according to a high-ranking D.C. school official.

Earlier this month, the firm's director, Brenda Strong Nixon, said in an interview that her firm occupied the building rent-free. Nixon could not be reached yesterday.

Andrew E. Jenkins III, deputy superintendent of D.C. schools, said the school system signed a lease with Nixon on April 1, 1980, and has billed the nonprofit corporation about $40,000 each year.

Associates for Renewal in Education has paid a total of $10,710 in rent in the past six years, and has gotten a $45,000 credit for "services rendered," Jenkins said.

Jenkins said he recently received a request from Nixon for more credits.

The firm received $1.2 million last month to train 5,000 teen-agers.

The District's summer jobs program, which Mayor Marion Barry said will employ more than 22,000 youths, is supported by $8.5 million in city funds and $8 million in U.S. Department of Labor money.