SOUTHEAST Asia is turning to former foes from both sides of the Cold War to help fill the growing regional security vacuum, as more countries rush to beef up their armed forces. The United States, Russia, Vietnam, China and Japan will all be asked to play a role in keeping the peace at talks in Singapore on Sunday that will seek a new balance of power to replace declining American influence. But analysts say the background of economic competitiveness between Asian states and fears of Chinese domination will make it difficult to head off an escalating arms race. ''Hopefully it won't ever come to that, but there's an awful lot of money being spread around defence suppliers: if you have a power vacuum, time is of the essence,'' said a European diplomat. The US and its Western allies - Canada, Australia, Japan, New Zealand and the European Community - will discuss security issues with the Association of Southeast Asian Nations (ASEAN) following the group's annual foreign ministers' summit. Russia, Vietnam, China, Laos and Papua New Guinea have also been asked along as ''guests'', and are expected to be formally invited to join future Asean post-ministerial briefings. The talks follow unprecedented spending on defence by Asian countries since the US closed its bases in the Philippines and signalled its intention to focus more on a domestic political agenda. China has purchased missiles, planes and rocket technology from Russia since the break-up of the Soviet Union, and is reported to be building an airbase near the disputed Spratly Islands. Despite denials of an arms build-up, analysts believe there is evidence that the purchases have acted as a spur to neighbouring countries. ''On the face of it, this is just a normal modernisation programme for countries that have neglected their defences while they were under the American security umbrella - it's a period of catching up,'' said the diplomat. ''But the danger is that these countries will eschew multilateral, collective defence for independent deterrents that are then perceived as a threat to other countries in the region.'' ASEAN took the initiative itself in March by drawing up a security agenda at a preparatory meeting for this weekend's Singapore talks, and widening the consultative net to include China, Russia, Laos and Vietnam. The four countries, whose communist insurgencies inspired the formation of ASEAN, are likely to be included in historic direct security talks at next year's foreign ministers' summit in Bangkok, after having observer status in Singapore. The spurt of diplomatic activity is aimed at plugging the security gap left by the US pull-out before it becomes a potential economic and political battlefield between China and Japan. ASEAN officials are anxious to draw Washington and possibly Moscow into new roles as strategic partners to balance the Chinese and Japanese influences. Russia, anxious to build on its increasing defence links in Southeast Asia, has told ASEAN it doesn't want to be left out of any security arrangement. The most reluctant partner is expected to be China, which has given weak assurances on shared development of the potentially explosive Spratly Islands, but remains aloof from security initiatives. While some ASEAN members believe shared economic development will inevitably draw Beijing into the fold, doubts linger over whether it can he trusted. ''The way to test China's sincerity is to make it a part of the dialogue. You don't achieve anything by leaving them outside,'' said an Asian diplomat.