Maryland Gov. Harry Hughes agreed today to defer signing an agreement with a contractor who is scheduled to begin vehicle emissions tests in the state next year after House of Delegates leaders asked to review the contract.

Hughes was scheduled to sign the contract at a Board of Public Works meeting today but agreed to wait until Feb. 18 after receiving a letter from House Speaker Benjamin L. Cardin.

Cardin said he is concerned that the vehicle-emissions-inspection program, which the state must initiate to comply with federal clean air regulations, is going to cost the state $3 million in its first year of operations. Originally, the program was to have paid for itself, based on a charge of $9 per inspection.

Hughes, faced with a controversial issue in an election year, agreed last winter to defer the start of the program until January 1984. Because of that delay, the cost of the program, according to Cardin, will be increased by $5.4 million.

The legislative leadership wanted to review the contract with a California-based company, called Systems Control Inc., to see if there were any ways to cut costs. One measure Cardin said he would definitely ask for would exempt indigents from having to pay for the cost of repairing a car that failed to pass inspection. At present, an owner whose car fails the inspection can be made to pay up to $75 for repairs.

The delay has already jeopardized economic development in the state because the Environmental Protection Agency has ruled that Maryland is one of 16 states that violated the Clean Air Act by not having a program in place by Dec. 31. A ban on growth against Maryland businesses will go into effect July 1 unless the state can show cause in the next 45 days why it should not.