American Management Systems Inc. (AMS), said yesterday that it has acquired Executive Systems Inc., a data-processing firm based in Bethesda, Md.

AMS, which in 1980 had revenues of approximately $60 million and employed about 1,000 workers, is a computer systems and services firm with headquarters in Arlington, Va. The firm it has acquired has revenues of approximately $1.8 million annually and specializes in providing data-processing services to associations and membership organizations.

AMS also announced that net income for the fourth quarter of 1980 declined 22.1 percent to $353,000 (20 (20 cents per share), compared with $453,000 (31 cents) during the same period in 1979. Net income for the year ended Dec. 31, 1980, increased to $2.149 million ($1.40), compared with annual earnings of $1.724 million ($1.21) in 1979.

San Juan Racing Association Inc. reported net income of $2.860 million (66 cents) for the nine months ended Jan. 31, 1981, compared with $2.013 million (47 cents) during the same period a year before. For the three months ending on that date, the company reported earnings of $230,606 (5 cents), compared with a loss of $128,163 (3 cents) during the same period a year earlier.

Those results include the impact of the discontinued operations of the Washington Diplomats Soccer Team, which was sold in October 1978.

The company owns and operates El Comandante Race Track in Puerto Rico and several radio stations including WUST-AM in Washington. San Juan Racing and Gulf United Corp. reached an agreement last August that provides for the acquisition by Gulf Broadcast Group Inc. of nine of the 10 radio stations.

USAir (formerly Allegheny Airlines) reported a net loss of $518,000 (6 cents) for February, compared with net earnings of $2.316 million (17 cents) during the same month a year before. The company blamed the February results on the impact of severe weather on traffic.

The company reported a loss of $1.388 million (16 cents) for the first two months of 1981, compared with earnings of $191,000 (and a loss per share of 3 cents) during the same period in 1980.

Survival Technology Inc. which designs and manufactures medical devices and provides services aimed at treatment of emergency health problems, announced that net income for the six-month period ended Jan. 31 was $221,800 (9 cents), compared with $737,600 (30 cents) during the same period last year.

The Bethesda firm said that net income for the three-month period ended on the same date declined to $40,500 (2 cents) from earnings of $262,200 (11 cents) a year before.

Company officials said the decline in income reflected a decline in sales as a result of a lower level of shipments of military auto-injectors and commercial syringe products.