The £75m earmarked in the Labour manifesto for the proposed social investment bank would not be enough to make the bank viable and sustainable, according to the Charities Aid Foundation.
Reacting to sector-specific proposals in the manifesto, CAF also said it would be interested to see more detail about a proposal to review incentives for philanthropy to arts organisations.
Stephen Bubb, head of chief executives body Acevo, said: "We welcome the strong theme of public service reform evident throughout Labour's manifesto, in particular the explicit references made to a greater role for the third sector. We are glad to see a commitment to encouraging a level playing field in the commissioning process reaffirmed.
"It is also reassuring to be reminded of Labour's recognition of the importance of the sector's independence, and in particular the value of its ability to campaign," he added.
Sector umbrella body the NCVO said proposals for greater strength for the Compact and the promotion of schemes to give communities greater control over local public buildings were "great news for the sector".
On the proposal that National Lottery money diverted to the Olympics would "return to culture, heritage and sport" after 2012, the NCVO said: "We would be concerned at any proposals to divert lottery money away from voluntary organisations."
The Community Development Finance Association welcomed the Labour manifesto's pledge to increase lending to poorer communities, to be paid for by a levy on banks, but said state funding was also needed.
The manifesto makes a pledge to "help fund a step change in affordable lending by third sector organisations" such as CDFIs, which provide loans to people who struggle to get the finance they need from banks. This was announced in the Budget last month.
Bernie Morgan, chief executive of the CDFA, said: "Labour has made a positive start. Now it's time for the other parties to say ‘see you and raise you'.
"As well as levying the banks, the next government should step up state funding for third sector lenders, as Obama's administration has done. Public finances may be tight, but this is a guaranteed way to create and save jobs, boost small businesses and support low-income families."
Co-operatives UK welcomed the commitment to mutualisation for pubs and football clubs and to opening up new possibilities for cooperative businesses, such as rail operators.
"Cooperatives have enormous potential to bring about a fairer society and the commitment across the manifesto to cooperatives and mutuals demonstrates that the Labour Party recognises this," said David Coulter, deputy chief executive of the organisation.
The Princess Royal Trust for Carers welcomed the proposal to establish a national care service, but said it was deeply concerned that carers would lose out if the current system of assessing state support were to continue.