The corps, a £21 million Government initiative to promote volunteering among over-50s, is broadcasting a TV campaign during July in the north of England.
With only nine months' worth of funding left, the corps, which was established in 2001, still has to attract another 115,000 recruits if it is to achieve its target of 250,000 by March 2004.
Andy Forster, information and policy officer at Volunteer Development England, an umbrella body for 345 volunteer bureaux, said no amount of marketing could mask the damage the corps had done to volunteering.
"It's bonkers spending £21 million on something the sector is already doing," he said. "The Experience Corps has failed to build on the existing infrastructure and has alienated the voluntary sector.
"Volunteering works locally: it doesn't work as a brand. The corps has made absolutely no impact on the number of older people coming to our bureaux."
Sue Evans, executive director of Reach, a charity that encourages professionals to volunteer, said it would be crazy to continue funding the corps, which employs 96 full-time staff, beyond 2004. "Small local agencies have achieved much more at a zillionth of the cost," she said. "The ad is a waste of public money and reflects the desperation they must be feeling."
Richard Lancaster, marketing director at the corps, said he was "pretty confident" of achieving the 250,000 target. "We only concluded our regional launches in June 2002 so we've only been a national organisation for twelve and a half months," he said.
Lancaster urged the Government to make a decision within the next month on whether to continue to fund the corps beyond 2004. "The Experience Corps is a brave experiment but one that we've shown can work," he added.
CSV, whose executive director Elisabeth Hoodless sits on the Experience Corps board, refused to speculate on the corps' future.