A STRICTLY ballroom spectacular will be one highlight of this year's Merdeka Ball, the Malaysian Association of Hong Kong's National Day celebration. The ball will be on this Saturday at the Marriott Hotel. Between 450 and 500 guests will enjoy a fine dinner, followed by quality entertainment from one of the territory's favourite performers, Maria Cordero. Vice-chairman of the association, P. O. Choong, said: ''The evening will also feature a ballroom dancing spectacular, a fashion show and an auction, at which we hope to have some rare antiques to bid for.'' The association's committee will be in regulation black-tie, but Mr Choong said: ''I don't expect to see many dinner jackets because the Malaysian people are not really very formal, although I am certain the ladies will be stunning.'' The ball is sold out, but three tables are in reserve if there is a late flurry of interest. The Malaysian Association had ''well over 1,000 members'', a very respectable proportion of the estimated 12,000 Malaysians in the territory, Mr Choong said. It met each Friday at the China Tee Club, first floor, Pedder Building, Pedder Street, Central. The club organised special activities at least once a month, not necessarily on Fridays. These might range from a karaoke night, to a country picnic, dinner parties, barbecues, boat trips or hiking. It was planning a trip to scenic Guilin, in China, for several days. Mr Choong said the association's official charter stated its purpose was to ''foster closer relations among Malaysians, and non-Malaysians, in Hong Kong''. But, he said: ''It's a very loose and informal organisation . . . people come and go all the time . . . just like Hong Kong itself, really.''