Martin Marietta Corp., bouyed by strong showings from its aerospace and specialty chemicals business, reported increased second-quarter earnings.

Net income was $61.1 million ($2.45 a share), compared with $58.8 million ($2.36) a year earlier. Sales were $889.2 million, compared with $643.8 million.

Net income for the first six months was $100.8 million ($4.04) compared with $93.3 million ($3.75). Sales were $1.6 billion compared with $1.2 billion.

The company said profitability of its aluminum, cement and aggregate business declined, and it finds few signs of encouragement in those areas in the near term. Its aerospace and specialty chemicals divisions, however, made strong contributions to the earnings picture.

Atlantic Research of Alexandria reported record second quarter earnings of $802,000 (43 cents a share), compared with year-ago earnings of $664,000 (41 cents). Revenues were $24.1 million, compared with $19.0 million.The average number of outstanding shares in the second quarter were 1,844,261 compared with 1,557,686.

For the six months ended June 30 net income was $1.6 million (84 cents), compared with $1.2 million (80 cents). Revenues were $45.8 million compared with $36.0 million.

American Management Systems Inc. of Arlington reported a loss for the second quarter of $229,000, compared with net income of $626,000 (42 cents) a year earlier. Revenues were $16.5 million compared with $14.1 million.

For the first six months the loss was $90,000, compared with net income of $1.2 million (78 cents). Revenues were $31.4 million compared with $28.0 million.