THERE was euphoria on the floor of the stock exchange as the Hang Seng Index finally broke the 10,000 mark, ending six months of trading in the four-digit zone. Even though the market was not able to maintain its momentum and slipped back to trade within the 9,000 level in the afternoon, brokers remained confident of further rises. The index closed the day at 9,962.04, a gain of 60.48 points, or 0.61 per cent. Volume was $4.94 billion. But all the action was in the morning session, when the Hang Seng burst through the 10,000 barrier just after opening. Lower-than-expected job figures in the United States were the precursor to yesterday's buying. With the pressure off interest rates, bond markets were able to rally and the outlook for world equities is now good. Hong Kong was one of the first markets in the world to open after the jobs figures came out and investors wasted no time in snapping up blue-chip stocks. ''All over the weekend there were lots of bullish arguments in the newspapers and sentiment was on the buy side,'' said a derivatives dealer. Renewed hopes on the airport talks also boosted confidence, although that was not a major factor singled out by brokers. Volume surged in the morning with $3 billion worth of stocks traded, backed up by strong buying on the futures market, led by Morgan Stanley. There were again rumours that Morgan Stanley's chief strategist Barton Biggs would raise his weighting for Hong Kong, but so far those rumours appear unfounded. The index slipped below the 10,000 mark in the afternoon, with volume much lighter at about $1.9 billion, as most buyers got their business done in the morning session. Futures also closed at a discount to cash and brokers were expecting the index to open slightly lower today. Baring Securities director James Osborn said: ''The signs are there for a push up to the 10,500 mark in the next four weeks, but progress will probably be a lot slower than many investors hope for.'' Volumes remain firm, but traders said progress would be slower and more volatile than last year when an international buying frenzy brought the market to a boil. The scene is fundamentally different to this time last year, when interest rates were falling and company earnings were rising. Another year on, and interest rates may have stalled, but they could still rise, and earnings growth is showing signs of slowing. W I Carr research manager Hazel Moore said the twin bogeys of rising interest rates and problems in the Chinese economy had subsided, but had not disappeared, adding that property remained vulnerable. But for the time being, investors are ignoring fundamentals and partying in the break before the next interest rate rise. There is a feeling that the best earnings growth rates in the world will be in Asia, and a lot of European and American funds are coming here on that basis. Hong Kong, being the proxy for Asia, excluding Japan, and one of the most liquid markets, will be absorbing more foreign capital in coming months, or until the next rate increase. Yesterday, trading moved in a 155-point range from 10,064.86 to 9,910.21. HSBC was one of the best performing blue-chip stocks, closing $1.954 higher at $91.50. The bank has been slow to move off the mark and there are still concerns as to its earnings. However, it is a core holding for any Hong Kong portfolio and should benefit on heavy buying from big fund managers. Cheung Kong shares remained flat at $39.50, although there was strong interest in the counter with $263 million traded.