The representative body wants the sector to discuss how to strengthen "micro-macro" relations between large and small charities in order to tackle the widening income gap that threatens to tear the sector into two.
Chief executive Stuart Etherington made the call at last week's NCVO annual conference, after research for the 2004 UK Voluntary Sector Almanac revealed the worsening financial plight of small and medium-sized organisations.
Between 2000 and 2002, charities with income above £1m grew, while smaller organisations saw their income fall. Most charities suffered an income drop.
Etherington warned that to split into two sectors would be "extraordinarily damaging".
"The almanac has shown that, while large national voluntary organisations have enjoyed a period of growth, small and medium-sized ones are operating in a much harsher fiscal environment.
"Our strength, influence and effectiveness as a sector lies in our ability to work together to achieve change. Therefore, the difficulties experienced by small organisations are an issue for the whole sector to consider and work together to alleviate," he said.
Etherington cited the federal structure of charities such as Age Concern as a positive example of co-operation between large and small organisations.
"Much of the sector grew from a grass-roots level, and many big charities operate federal structures in which semi-independent local bodies provide the real hands-on work in the community," he said.
Kevin Curley, chief executive of the NACVS, the umbrella body which looks after the interests of smaller charities, welcomed the proposal for a summit meeting.
"The funding environment has become much more difficult over the past decade. Many of the small grants schemes run by local authorities and health authorities have disappeared to be replaced by contract arrangements that favour larger organisations," he said. "Fundraising from the public has become more difficult as a result of tighter regulation on food hygiene, community centre licensing, criminal records checks and so on - and huge increases in the costs of insuring events."
Etherington used his speech at the conference to argue that, despite its growth in size and influence over the past decade, the voluntary sector was "still not fully at the table" in its relationships with government and business. "We are still not truly taken seriously," he said.
"We have to fight every inch of the way for every gain. It still doesn't come naturally to any of the other sectors to treat us as an equal."
Etherington urged the sector to develop a greater confidence in itself.
"I think in many cases our problem has been that we have accepted the role of junior partner, when in fact we should have been prepared to make our case more strongly," he told the conference.