Fairchild Industries has cause for hope today after two congressional committees took favorable action on funds for the company's T46A jet-trainer program.

First, House and Senate members late Wednesday night postponed a decision on permanently withdrawing $170 million in the 1986 budget for the jet until the 1987 defense budget is decided. That left open the possibility that Fairchild would receive money to build 22 planes.

In a separate action, the House Armed Services subcommittee on procurement approved $100 million to build 12 planes in the 1987 fiscal year.

"The fact of the matter is that the Air Force does want it," said Rep. Sam Stratton (D-N.Y.), chairman of the subcommittee. "The people in the Air Force and the Training Command . . . and the pilots themselves want a plane that is up to date, modern, and not . . . old technology." Stratton said he expected House support in authorizing and then appropriating the money.

Fairchild could not be reached for comment late yesterday. The Air Force has called the jet a "good airplane" but has said it will oppose funding it if Congress suggests the removal of a higher-priority fighter system as a way to fund the trainer program.

A clash between the House and Senate is expected over the trainer since the Senate has left it out of its defense authorization bill. The House and Senate will likely debate the trainer's funding later this summer.

"The effort to save the T46 is strengthened by this latest battle," said Rep. Thomas J. Downey (D-N.Y.). "By keeping the 1986 funds alive, we've ensured that Fairchild Republic will remain vital so that we can fight the next battle."

Initially, Fairchild was to receive $3.5 billion to make 650 jets to replace aging Cessna T37 trainers. But, the Air Force proposed dropping the plane out of its 1987 budget after finding "numerous management and production deficiencies" at the Long Island division that makes the plane. Those problems are largely solved, according to Fairchild. So far, Fairchild is being paid to make 10 jets and two test craft.

Fairchild suffered a loss of $167 million in 1985 because of its troubled aircraft manufacturing business and had to sell its 50 percent stake in two profitable communications ventures -- American Satellite Co. and Space Communications Co. -- to offset some of those losses.

But Fairchild, which wants one-third of its diversified business to come from communications in the next five years, yesterday announced its first major piece of business in the area of shared-tenant services. Shared-tenant services provide tenants in office buildings with voice, data and video communications services on a shared basis.

Harold Gruen, president of Fairchild Communications Networks and Services Co., a Fairchild division, said a contract had been signed with J. T. L. Tycon Developers to provide shared services for three 17-story JTL Tycon Towers office buildings at Tysons Corner.

The first of the three office buildings will be ready for occupancy this year, and Fairchild hopes to have leased services there to 90 percent of the tenants by the beginning of 1988.