LAMMA residents, environmentalists and archaeologists are claiming an unprecedented victory over the owners of the Lamma power station, following a decision by Hong Kong Electric to scrap its plans to build a storage site directly behind the island's mostpopular beach. Lamma residents and environmental campaigners bombarded the Government with petitions and letters objecting to the company's proposals for the construction at Tai Wan To beach. They said rare nesting grounds and an archaeological site would be ruined if the developers received the go-ahead to build on 1,800 square metres of ''virgin'' land. Residents also feared the beach would become inaccessible if planning permission was granted. And archaeologists were angry when a Government official was quoted as saying the archaeological site was ''not of any great importance'', a statement which protesters claimed could not have been further from the truth. The site, now designated a site of special archaeological interest (SSAI), was first discovered in 1932 and ranks among the 10 most important in Hong Kong. Several digs have taken place and a number of bronzes - daggers, axes and arrow tips - dating to 1,000 BC have been unearthed. The most recent investigation was carried out in 1991 when some of the most significant artefacts were found, including a jadeite ceremonial sword and a sceptre from the Bronze Age. ''This site is extremely important and if the proposal had not been brought to the attention of the press the development could have slipped through and that could have ruined the site,'' said William Meacham, chairman of the Hong Kong Archaeological Society. Protester Liz Gower, who has lived on Lamma since 1986, said: ''I am so thrilled, it is just starting to sink in that we have won. We will have to hold a big party to celebrate. ''At first it felt as though we were in a losing battle. No one appeared to be listening to our complaints; it was like beating our heads against a brick wall.'' Furious residents gave the District Lands Office an ultimatum two weeks ago to meet them to discuss the project or face mass protests. The applicants, Japanese construction company Nishimatsu acting on behalf of Hong Kong Electric, initially said the site would be convenient due to its proximity to the power station. The storage plant would have been used to store building materials for the construction of two generator units at the power station. But yesterday a spokesman for Hong Kong Electric confirmed the plans had been withdrawn. ''We have discussed this at great length with Nishimatsu, and we both believe an alternative site would be the right answer. ''Our decision was due to the number of objections and the archaeological site.'' The spokesman said the company had yet to choose an alternative location for the storage depot.