The continuing success of Martin Marietta Corp.'s aerospace ventures offset sluggish performance by the company in aluminum and other housing-related markets and led to a 18 percent rise in the company's third-quarter profits, the Bethesda firm announced yesterday.

The company reported profits of $60.58 million ($1.62 a share), up from 1980 third-quarter profits of $51.34 million ($1.37). Although the figures take into account a 3-for-2 stock split completed this week, profits on a pre-split basis were $2.42 for the quarter, up from $2.06 last year. Sales for the quarter rose from $697.43 million last year to $835.94 million this year.

Nine-month sales for the conglomerate are $2.43 billion, up from $1.9 billion for the same period last year, while profits rose to $161.42 million ($4.31) from $144.64 million last year.

In other reports, TransTechnology Corp., reported profits for the second quarter of its fiscal year of $659,000 (24 cents a share), up from $424,000 (18 cents) last year, although revenue dropped from $11.24 million last year to $10.65 million for the quarter. Profits for the first half rose to $1.48 million (53 cents) from $906,000 (43 cents).

Isomet Corp. of Springfield reported third-quarter profits of $251,000 (16 cents a share) on sales of $1.25 million. Both figures were improvements over comparable 1980 sales of $910,000 and profits of $215,000 (15 cents).

Nine-month profits rose sharply to $783,000 (51 cents) this year from $394,000 (51 cents). Sales are up to $3.24 million from $2.14 million.

A. H. Robins Co. reported third-quarter profits of $9.69 million (39 cents a share) compared with $9.51 million (38 cents) a year earlier. The company reported flat sales of $113.84 million, $545,000 more than during the 1980 third quarter.

For the first three quarters of the year, the Richmond-based firm reported profits of $27.58 million ($1.10), up from $25.44 million last year.