Martin Marietta Corp. yesterday detailed a record $401 million capital investment budget for 1982 and forecast that profits in the year now ending will be up modestly.

Chairman J. Donald Rauth said the diversified Bethesda industrial firm is shifting its investment emphasis somewhat to focus on its booming aerospace business, which is a major industrial participant in the Space Shuttle program and a developer or builder of missiles, munitions, communications equipment and military electronics. That division's investment budget for next year will be $207 million, or more than half of total outlays.

Well over $80 million will go to buying land and constructing facilities in Orlando, Fla., for several Martin Marietta advanced electronic manufacturing programs on the threshold of production. Extensive missile production work already is centered at existing facilities in Orlando and Ocala, Fla.

Rauth said other aerospace spending will provide specialized facilities for growing workloads at Martin Marietta's operations in Baltimore and Denver. He also revealed that overall aerospace sales this year will be $1.9 billion, compared with $1.2 billion last year and a nearly three-fold growth over the last four years.

Largely because of aerospace earnings this year, Martin Marietta profits will be a record--up some 5 percent from a year ago to about $5.30 a share, Rauth said yesterday. That figure translates to about $8 a share before a 50 percent stock dividend on Oct. 19, compared with $7.55 a share in 1980, when total earnings were $188 million on sales of $2.6 billion.