SINGAPORE'S economy grew at a cracking pace of 10.1 per cent in the second quarter, exceeding all expectations and achieving a result not seen for four years. Announcing the figure in his National Day message, Prime Minister Goh Chok Tong said growth for the first half was 8.7 per cent. The Ministry of Trade and Industry was projecting an expansion of 7.5 to eight per cent for the whole year, he said. Analysts had been predicting a second-quarter result similar to the 7.1 per cent recorded in the first quarter. While signs that the economy was doing well in the second quarter had led to annual forecasts above the Government's earlier six to seven per cent projection, all were well below eight per cent. After overheating to 11.1 per cent in 1988, Singapore's economy grew at a declining rate through 1989 (9.2), 1990 (8.3), 1991 (6.7) and 1992 (5.8). It began last year sluggishly, with a low point of 4.7 per cent in the second quarter, but gradually picked up steam with a fourth quarter rate of 7.4 per cent to give 5.8 per cent growth for the year. Strong demand from Singapore's major markets - the United States, the European Community, Malaysia and Japan - produced a 21.3 per cent increase in the volume of non-oil domestic exports during the first half, representing a more than threefold increase over the same period last year. Analysts expect a slackening in exports of computer and electronic products - which were mainly responsible for the rise - in the second half but while the export sector may weaken, domestic demand is expected to remain strong. Mr Goh gave three main reasons for the good results: the region was prospering and Singapore was prospering with it; Singapore had stayed competitive, even though its costs had ''gone up somewhat in recent years''; and ''we have been nimble enough to seek out new opportunities and take advantage of them''.