The mayor and City Council speaker’s plan to bring 1,000 new fruit cart vendors to poor neighborhoods is drawing glowing praise from health advocates and bitter criticism from supermarket owners and grocers. The two camps will hold dueling demonstrations on the steps of City Hall today, aiming to influence a council committee’s vote on the bill scheduled for Wednesday.

Mayor Bloomberg and Speaker Christine Quinn announced the cart proposal in December as a measure to combat what the health commissioner, Thomas Frieden, described as the city’s “obesity epidemic.” Under the plan, 1,000 carts would be disbursed during a two-year period with permits to operate in police precincts that the city deems as having insufficient access to fresh fruits and vegetables. The legislation faces a backlash from businesses and council members who say the carts represent unfair competition.

“The theory behind this bill is if you increase the supply, the demand will increase, and that’s likely a faulty premise,” Council Member John Liu of Queens said in an interview yesterday. “If there was demand, it’s doubtful that the stores would simply refuse to address it.” He called the legislation “wishful thinking,” and warned it would eat into existing grocers’ profits without providing its intended health benefits.

Today, Mr. Liu, who sits on the committee that will vote on the bill, and several groups representing supermarkets and Korean grocers will protest the legislation outside City Hall. Proponents of the bill are responding: A coalition of more than 100 child advocacy, hunger action, and health groups are organizing a rally today at City Hall in support of the bill.

“There is a health crisis in many of these communities — diabetes, obesity, heart disease — that could be effectively combated if consumption of fruits and vegetables was improved upon,” the executive director of Citizens’ Committee for Children, which is participating in the pro-fruit cart rally, Jennifer March-Joly, said yesterday.

Ms. March-Joly described grocers’ fears of being undercut by fruit carts as unfounded. “We’re targeting areas where supermarkets are virtually nonexistent and the stores that do exist are not selling produce,” she said. “In no way would a cart compete with a grocery store.”