INVESTOR appetite for Hong Kong dollar debt securities seems undiminished by the United States' budget problems, with Hong Kong dollar issues by Brierley Investments and the Exchange Fund being placed easily. Bankers said Brierley's first issue of Hong Kong dollar debt - a $1 billion floating-rate note - went ahead yesterday. The notes pay interest of 82.5 basis points over the three-month Hong Kong interbank offered rate, and were issued at par. The Hong Kong Monetary Authority said its usual weekly offering of $1.5 billion 91-day bills attracted more than $7.5 billion in bids. Applications totalled $7.59 billion and the Exchange Fund allotted $1.5 billion at an average accepted yield of 5.49 per cent.