The Air Force has delayed the date on which the secret Stealth bomber will be become operational, perhaps more than a year, because of technical and production problems according to sources familiar with the program.

Congress ordered the Defense Department last year to push back initial operational plans for the Advanced Technology Bomber if its prime contractor, Northrop Corp., encountered problems producing the craft.

It is designed to evade enemy radar because of its unusual shape and construction materials.

The Air Force also will delay for several months the first test flight of the bomber, according to congressional sources and Northrop employees.

That had been scheduled this spring, sources said.

In addition, the Air Force is withholding some payments on the aircraft to Northrop because of the company's problems in managing subcontractors on the project, according to an Air Force spokesman.

Northrop had requested that the payments be withheld until the problems are resolved, the spokesman said.

Air Force and Northrop officials refused to disclose the amount being withheld.

The Defense Department has stopped more than $130 million in payments to Northrop for serious production problems with the guidance system of the MX intercontinental ballistic missile.

The full Stealth bomber budget has not been publicly disclosed because the aircraft is one of the military's most secret programs.

Former defense secretary Caspar W. Weinberger said developing and building 132 of the bombers would cost about $36.6 billion in 1981 dollars, a figure expected to increase substantially because of inflation and the plane's technical problems.

Northop and congressional sources, who asked not to be named, said the Stealth bomber program has been troubled by production problems for months.

Congressional demands that Northrop solve those problems rather than race to meet production deadlines were prompted by technical problems that have sharply limited capabilities of the B1 bomber.

Although the B1 force became operational on schedule in the fall of 1986, the Air Force has not figured out how to fix technical problems with its sophisticated electronics systems.

Problems with the B1, as well as Northrop's MX production facilities, also led Congress to impose stricter legislative controls over the Stealth bomber, which has been designated the B2.