GENERAL MACARTHUR'S HEADQUARTERS, Melbourne -- A threat to Port Moresby, chief allied outpost in New Guinea, dwindled Monday night with reports that Japanese troops have fallen back on Lae, 195 miles north, after clashing with Australian jungle fighters at the high tide of a 27-mile advance up the Markham valley.
Another potential menace to Port Moresby persisted, however, in unexplained Japanese operations 15 miles south of Salamaua in the coastal area of northeastern New Guinea. Salamaua is 165 miles due north of Port Moresby, which lies across Torre strait from the Australian mainland.
(The German-controlled Paris radio quoted Tokyo reports that the Japanese have launched a "violent offensive in the direction of Port Moresby." It reported the Markham valley advance and said the column pushing down from Salamaua was battling Australian troops, who were fighting a rear-guard action.)
Jap planes downed
General Douglas MacArthur's headquarters, silent on the New Guinea situation, announced that the American-Australian air force destroyed or damaged five more Japanese planes, including a big flying boat, and scored bomb hits on a third enemy transport in a new broadside over the northeastern war zone.
Twelve Japanese bombers, escorted by eight Zero fighters, raided Port Moresby Sunday, the united nations communique revealed, and in "brilliant" counterblows allied fighters destroyed three bombers and one fighter with only slight losses.
Striking at Rabaul, New Britain, for the second time in a few hours, allied bombers Saturday night dropped bombs Saturday night dropped bombs squarely on an enemy transport in the harbor where earlier in the day they had damaged two transports and capsized a tender.
Flying boat damaged
Two long-range bombers on reconnaissance Sunday engaged a four-motored Japanese flying boat and badly damaged it in a running battle.
An official Australian war correspondent reported from an advance allied base that the Japanese force which struck out from Lae through the Markham valley had returned to its base after advancing as far as Nadzab.
Five weeks ago the Japanese pushed up the valley to the same point, only to be washed all the way back to the coast by a deluge which turned the valley into a vast lake.
Other reports from the north said the "strong" Japanese force made contact with Australian troops in the Markham valley, but it appeared that the clashes were between units of semi guerilla fighters.
The recent intensity of the air war over the New Guinea area, together with stern warnings by Australian and allied officials that Japanese action might be expected at any time, supported predictions that Port Moresby might be in for attack.