Musical about German flying ace von Richthofen seldom rises far off ground; The Death of von Richthofen as Witnessed From Earth Play with flying and songs. Written, composed, and directed by Des McAnuff.

In his first major original work, Des McAnuff has imagined nothing less than the relationship between the legend of Germany's greatest World War I flying ace and the rise of Adolf Hitler. The nightmarish vision involves an awesome array of stage gadgetry and special effects, including mobile aircraft. The dizzying hypothesis needs only the Ronald Searle caricaturist's touch to invest the show with the kind of craziness appropriate to its outsized dimensions and theatrical aerobatics.

In terms of substance, ''Von Richthofen'' is less impressive. Furthermore, because of its weight - and length of takeoff - the surrealistic flying machine seldom rises far above the earth from which the events are witnessed.

An audience assembling at the Public/Newman Theater immediately undergoes a realistic baptism of fire from the sound-effects department. This is followed by an opening scene with bombs bursting in air and elsewhere on Douglas W. Schmidt's realistic-fantastic 1918 setting. After the bombardment, a British aviator (Robert Westenberg) descends from the skies and pauses mid-plunge to sing the jaunty ''All I Wanted Was a Cup of Tea.'' He is accompanied on the piano by the ghost of an Australian NCO (Marek Norman) who has perished in the preceding barrage. Such irony and mordant humor serve as the principal medium for the McAnuff message.

The main action of ''Von Richthofen'' occurs in two sectors of the multilevel setting. The sandbagged dugout on the left is occupied by Australian Pvts. Robert Buie (Robert Joy) and William Evans (Mark Linn-Baker), whose Lewis machine gun may or may not be operational. The inept Buie and Evans relieve the boredom and terrors of battle by dreaming of their postwar careers as a team of bemedaled vaudevillians and practice music-hall routines.

Across the stage, separated by a scarred no-man's land, are von Richthofen's luxurious quarters, scene of the events immediately preceding the Red Baron's fatal last flight. As his own mythmaker, Mr. McAnuff embroiders the mystique surrounding the German ace's 80th kill (after which he is being urged to retire into folk legend and leadership).

No one can deny Mr. McAnuff's flair for fantasy. ''Von Richthofen'' is an enormously complex series of fragmented scenes and songs, with the musical numbers intrinsic to the overall dramatic scheme. The generally agreeable, sometimes reminiscent score ranges from music-hall patter songs and martial chorales to von Richthofen's wistful memory serenade to Sarah Bernhardt.

In the central role, the excellent Mr. Vickery matches the Prussian arrogance and antiheroic panache of the blond Teuton with what Mr. McAnuff presents as a pragmatic realism. Mr. Vickery's problem in delineating the role would seem to stem from Mr. McAnuff's problem in fashioning it.

''Von Richthofen'' reflects a number of influences, from Bruce Bairnsfather to Brendan Behan, from Brecht and Weill to Joan Littlewood and beyond. To say so is no reflection on Mr. McAnuff's own inspiration. That this ''play with flying and songs'' seldom reaches the heights intended is not for want of genuine creativity or lavish investment.