DELEGATES from China and Taiwan drank a champagne toast to closer ties embodied in four agreements signed at the end of a landmark meeting in Singapore yesterday. After a simple ceremony, which had been postponed for one day because of sharp differences over economic issues, Mr Koo Chen-fu, leader of the Taiwan team, said: ''We have laid a good foundation for the future development between both sides. And this indeed is of very great significance.'' His opposite number, Mr Wang Daohan, said the talks have achieved a ''win-win'' result. Playing down the existing differences between the two sides, he said they would have to make preparations before returning to the negotiating table for more consultation. ''This is just the beginning,'' said Mr Wang, a close friend of Communist Party chief Mr Jiang Zemin. The two leaders left out the contentious issue of how to protect Taiwanese investments on the mainland in the ''joint accord'', which was signed with three other documents. The documents cover the handling of lost mail, verification of lost mail, and the setting up of a system of contacts between the two semi-official bodies - Taiwan's Straits Exchange Foundation and the Association for Relations Across the Taiwan Strait.