An ambitious application calling for a mixed-use, 3.5-story building to be constructed at 16 Cross St. encountered questions about intensity of site development, timing and potential for precedent during a first public hearing on the plan Tuesday night by the Planning and Zoning Commission.

The proposed building would have underground parking, and encompass about 7,000 square feet of commercial space on the first floor and about 8,000 square feet of residential units on the second, third and fourth floors. But in order for the project to be considered by the commission, the developer, 3M Capital Trust LLC, also is seeking multiple amendments to the town's zoning regulations.

Commission member Dick Ward said the Cross Street area does need to be renovated, but he warned the applicant that the commission would need time to evaluate the consequences of approving the project.

"I think most people agree that that's an area that's not going to appear on House Beautiful (magazine) anytime soon," he said of Cross Street. "But whatever we adopt as changes now will apply to that whole area and we want to be comfortable and the town would want to be comfortable that it's appropriate for that area."

Stephen Finn, an attorney representing the applicant, throughout his presentation said the plan conforms with suggestions outlined in the latest Plan of Conservation and Development, which was adopted in August.

"You're in sort of early, but you're also in with something that the town's very interested in," Ward told the applicant. "That's fine. I think it's going to push us to act more quickly than we intended."

Finn argued that the development would represent a significant improvement over existing conditions, enhance the character and beauty of the downtown area, provide needed residential units downtown, provide for a diversity of housing options in a mixed-use building and perhaps provide space for a new post office location.

The LLC principal -- Arnold Karp, of Karp Associates -- told the commission that he'd like to have the New Canaan Post Office as his "anchor" tenant. He said he's asked Postal Service officials to consider the site, but hasn't yet heard a definite answer.

"They're interested; they're not interested. They were interested last week," he said. "We're trying to design a building that could accommodate them."

A Postal Service spokesman denied earlier Tuesday that the agency ever negotiated with Karp.

"Cross Street is not doable for us because there is a serious safety issue that we feel would put the community at risk," Christine Dugas told the New Canaan News. The biggest problem, she said, was that the site would require the mail truck to back up from or into the street, causing a safety hazard, particularly for pedestrians.

"The truck bringing the mail is quite large and there's not enough space for them to bring the truck in and maneuver," Dugas said. "It's too big of a risk."

The trucks are about 30 feet long and would pick up mail at least three times a day, according to Dugas.

If post office officials don't agree to reconsider the site, Karp said he would try to get two or three commercial tenants on the first floor and add more residential units there.

Among the various requests in the application, Karp is asking for a special permit in order to build special residential units in the Business B zone; permission to increase the building height and the number of stories for that zone, and a relaxation of the landscape standards. Additionally, the applicant seeks text changes in the zoning regulations to allow the project to be exempt from floor area ratio requirements, to allow a reduction of up to 25 percent of the required parking spaces for "an anchor use," to authorize the commission to reduce the minimum vehicular aisle width for parking spaces for two-way circulation and minimum stall depth by special permit.

"Approving these text changes in no way opens up a Pandora's box or requires the commission to grant any special exceptions in regards to increased height or number of stories," Finn told the commission, adding that all exceptions would be classified as special permits, which would have to meet a number of criteria, such as making sure the building height is in harmony with the area.

However, several commission members were concerned with precedents the project could set.

Michael Crofton, for instance, noted these are "brutal" regulation changes sought by the developer.

"If this is the tipper that's going to set the standard, we have to really be very careful about changing the regulations," he said.

Crofton also took issue with the fact that the developer is using the recently adopted POCD to justify the changes.

"What the POCD says is that we should consider making such changes," he said. "Is this not premature that we are being asked to make an affirmative finding of harmony and of being in keeping with our vision when neither of those factors actually exist yet?"

Chairman Lazslo Papp said the commission has no issue with increasing the number mixed-use developments in town. However, he said, "What you have to do is convince the commission of the size and the intensity of this proposal."

Michael Sweeney, an attorney representing Santo and Lynda Silvestro, who own eight properties on Cross and Vitti streets, urged the commission to take its time considering the consequences of the project and discussing them with neighbors.

"There hasn't been enough time to fully digest what the ramifications of these changes would be in the business B zone," he said.

Meg Paladino, whose father owns a property on Cross Street, said the project has a potential to increase parking problems in the area.

"I don't want the existing businesses to pay the price if there's an overflow of traffic," she said.

noliveira@bcnnew.com, 203-330-6582, @olivnelson