THE United States is maintaining its opposition to a substantial increase in the capital base of the Asian Development bank, suggesting instead the bank exercise thrift. However, pending a review, it does not appear to have completely closed the door on the issue. ''The bank must be thrifty. It need not and it cannot go on rapidly increasing its lending year by year,'' said Jeffrey Shafer, this year's ADB governor for the US. Mr Shafer yesterday called for an independent commission to review the bank's portfolio, expressing concern over the quality and success of some its previous lending. A spokesman for the United States official delegation to the ADB's 26th annual meeting being held in Manila, later said such a review would increase the credibility of the institution and in doing so make it easier for Congress to approve any increase in ADB funding. ADB president Kimimasa Tarumizu has been well aware of member concerns and already set up an internal task force to assess projects. However, Mr Shafer said: ''The best approach would be to commission an independent review of the bank's portfolio in order to further demonstrate the institution's openness and transparency.'' ''Donor country resources are limited and the bank's internal evaluation process is indicating that the payoff in development terms from projects is slipping.'' The ADB could be theoretically forced to start cutting back on lending to developing economies, such as China, next year if it cannot overcome Washington's resistance to doubling its capital base from 1994 to 1998. Mr Tarumizu and the ADB management have asked for a capital increase of between 90 and 120 per cent, providing the bank with a further US$30 billion to lend. This would allow lending to rise by between 10 and 15 per cent a year. China, which is expected to receive a record $1 billion or more in loans this year, would be one of the biggest losers if the increase were blocked. While Japan supports a capital rise, it has avoided a direct clash with the US on the matter. Hongkong ADB governor for this year Joseph Yam Chi-kwong supported the widespread call for a capital base rise, saying Hongkong had a vested interest in seeing China and the rest of the region prosper through increased ADB help. Mr Yam, chief executive of the recently-formed Hongkong Monetary Authority, said China particularly needed the ADB's technical assistance in creating banking systems with a high level of integrity to attract more foreign investors. ''If China creates a good financial system to assist in economic development, it must help Hongkong,'' Mr Yam said. Formal negotiations on the size of the ADB's fourth capital rise should start shortly after the annual meeting which ends today. The United States yesterday pledged continued support for the ADB but told delegates at the bank's headquarters in Manila its financial resources should be kept as what it described as a ''sustainable'' level. Analysts said the ADB had hit its sustainable lending level back in 1991, so if this policy were adopted it would mean cutting back to this level. On a political note, every year the ADB insists on referring to Taiwan in all its official documentation as ''Taipei, China'' to keep China happy and every year Taiwan protests. At last year's annual meeting in Hongkong, the Taiwan delegation went as far as to block out the country name card positioned in front of their ADB governor using masking tape. There has been no repeat of this stunt this year - perhaps a signal of improved Sino-Taiwan relations following recent talks in Singapore.