Fleeing Indochinese Often Rebuffed by Passing Ships
Over last few mos ship captains on high seas have been passing up boatloads of Indochinese refugees as nations in area become more reluctant to grant refugees haven; Panamanian freighter that picked up 31 Vietnamese refugees more than 2 mos ago is reptd on way to Japan after refugees were refused admittance to Singapore and Yemen; refugee sources say some cases of ignoring refugee appeals on high seas has led to violations of internatl seafaring traditions and laws that require aid to foundering (M)