The Amateur Athletic Foundation of Los Angeles, charged with disseminating funds from the 1984 Olympic surplus, has announced nearly $414,500 in new grants to Southern California youth sports groups.

The largest grant, $125,000, went to the Southern California Tennis Assn.'s National Junior Tennis League. Another $109,790 went to three velodromes in Carson, Encino and San Diego, and $72,000 was awarded to the Mt. San Antonio College Youth Days program to provide track and field instruction.

Other grants included $53,166 to the Boys and Girls Club of National City and $4,000 to sports programs in San Bernardino, Hawthorne, El Rio, El Segundo, Saugus, Glendale, San Gabriel, Santee, Sherman Oaks, West Covina, Pasadena and Los Angeles.