The cost of the government's National Citizen Service volunteering scheme is not justified at a time when youth services are being cut, MPs have said.
The education select committee said in a report that services for young people faced "disproportionate" cuts.
It estimated that offering NCS to all young people would cost more yearly than 2009-10 youth services spending.
The government said the money for the NCS was extra and it was consulting on a new vision for youth services.
The programme has been championed by Prime Minister David Cameron as a type of "non-military national service" to encourage young people from different backgrounds to mix.
It aims eventually -through external providers - to offer every young person in England the opportunity to attend a two-week residential, outdoor activities course and to spend a further three or four weeks working on local community projects.
But the committee, chaired by Conservative MP Graham Stuart, said the current cost for pilot schemes was £1,182 per young person - whereas Germany provided an entire year's volunteering for just £1,228 per participant.
"We do not see how the government can justify spending the same for a six-week programme," the MPs said.
The government has dedicated £13m for the scheme in 2011, and £37m in 2012, aiming for 10,000 participants this summer and 30,000 next year.
But the select committee estimated that, given the government's aim to offer the scheme to all teenagers, if half chose to participate, the total cost could amount to £355m per year.
That is more than the £350m spent in total on youth services in 2009-10, the MPs pointed out.
"Given the degree to which year-round youth services are being cut, and in light of our concerns about cost and practical implementation, we cannot support the programme's continued development in its current form," the report concluded.
It said there had already been "very significant, disproportionate" cuts to local authority youth services, ranging from 20% to 100% of spending.
It cited David Wright, the chief executive of the Confederation of Heads of Young People's Services (CHYPS), who spoke of a "double whammy" to youth services, with ring-fencing removed from previously allocated funding sources, in addition to overall cuts of 28% over the next four years to local authority budgets.
Dedicated youth-services funding has been amalgamated with other grants into an Early Intervention Grant - which itself is 10% less than the total of the funding streams it replaced, the MPs said.
They cited a survey by the CHYPS in February 2011, which found that cuts to youth services averaged 28% and some local authorities were cutting 70%, 80% or 100% of their services.
Cuts totalling more then £100m were planned by March 2012, and open-access youth clubs and centres were hardest hit, the study found.
The committee's report also cited a Department for Education document which said local authorities in many areas were cutting youth projects in favour of protecting early-years and child-safeguarding services.
The budget reductions "may be both dramatic and long lasting", the MPs said.
"The government's lack of urgency in articulating a youth policy or strategic vision is regrettable, is compounding an already difficult situation, and should not be allowed to continue," the committee said.
The MPs recommended that the National Citizen Service scheme be turned into an accreditation scheme for existing youth-development and volunteering programmes, and that the funds earmarked for it be diverted into general, year-round youth services.
In response to the report, Children's Minister Tim Loughton said he was "disappointed" that the committee had "sought to undermine the NCS pilots before they have even got off the ground".
It said the funding for the scheme was "additional money for youth services, not an alternative to them".
"Local areas need to think more creatively about how they do this and consider what more the voluntary and community sector can provide," he said, adding that the government was consulting on a "new vision" for youth services to be published in the autumn.
He also said it was "a shame" that the committee did not hear from many young people, including those who took part in the NCS, who "universally said they benefited enormously from the unique experience".