The Government's other support partners, Act and United Future, have opposed the legislation, meaning National needs the Maori Party's two votes to progress the law changes.
Failure to get the Maori Party's agreement would be a blow to Smith and the Government, who have been trying to advance the second tranche of RMA reforms for two Parliamentary terms.
The proposed changes, which affect environmental and planning decisions, are seen as crucial to making housing more affordable in New Zealand.
The Maori Party's support was initially secured in November after National made concessions around the way iwi were involved in the planning process.
However, Maori Party co-leader Marama Fox said in December the party was reconsidering its vote after it had been made aware of the way it could affect councils' decision-making.
Smith said there would be further talks between him and the Maori Party co-leaders.
"The Government has a policy agreement with the Maori Party over the progress of the second and third readings.
"The next stage, when the Bill is reported back, is for there to be discussions between the two parties on the legislative detail to ensure it is consistent with the agreement.
"This is a large, complex Bill of over 200 pages and the detail of the drafting is important."
He said on the weekend he expected to have the reforms passed into law in March.
Smith has pointed to the Auckland Council being challenged in court by Auckland Hospital and the University of Auckland because its ban on GMOs could prevent the Pexa-Vec liver cancer vaccine treatment of patients in the city.
If passed into law, the reforms will also allow homeowners to carry out minor renovations such as extending their deck or building a fence without a resource consent.