Goaded by news that eight-pound chunks of plaster were falling from the rain-soaked ceiling of Union Station and that the 73-year-old national landmark has been closed indefinitely for safety reasons, Congress yesterday began yet another attempt to salvage the rotting terminal as a usable train station.

Sen. Daniel P. Moynihan (D-N.Y.) introduced in the Senate a $40-million bill to repair the station's leaky roof, renovate the building, lease space for shops and restaurants and move the railroad tracks back where they once were when Union Station was considered one of the finest, most convenient train terminals in the world.

"What we propose today is primarily to return the building to its use before the Congress began fumbling with it." Moynihan said in a written statement. He apologized to the Senate for bringing up a new Union Station bill -- the fourth such measure to come before Congress in the last four years, all unsuccessful -- but said the deteriorated condition of the station required prompt action.

Meanwhile, in the House yesterday, Rep. Sidney Yates (D-Ill.), chairman of a subcommittee that could approve emergency repair funds for Union Station, called for special hearings today to find out why there is not enough money to fix the building's roof. A $2-million effort to fix a small part of the leaky roof is now only 5 percent complete and will not be done until the end of June.

During its 13-year involvement with Union Station, Congress has spent or committed itself to spend $117 million in the conversion of the once-colossal station into the National Visitor Center. Marked by outright deception, bad judgment, cost overruns and bureaucratic fighting, the Union Station affair has unfolded as an almost unparalleled example of congressional bungling.

"I know it is distasteful to many of my colleagues even to consider the Union Station situation. It is true that altogether too much time and money have been spent on this building," Moynihan said. "Unless we want to allow the building to become a ruin, we must do something."

For today's special House hearings, Russell Dickinson, director of the National Park Service, which runs the station for the federal government, has been called to explain why Union Station is falling apart.

The major reason, according to the park service, for the rotting condition of the station is that Congress has refused to come up with any money to fix it. Last year Congress authorized $11 million to repair the roof and pay for other structural repairs, but the money has not been appropriated and is not listed on any proposed budgets before Congress.

Longtime government participants in the Union Station fiasco said yesterday it is unlikely that the Reagan administration, in its fervor to cut the federal budget, will go along with spending money for a train station.

"If the building fell down, the Reagan administration would breathe a great sign of relief because then they wouldn't have to spend any money," said one high-level source.

The station, which was declared unsafe and closed on Monday as heavy rains poured through the roof, will be closed indefinitely because of fear that chunks of falling plaster from the 96-foot-high ceiling in the main waiting room of the station could cause serious injury, according to the park service.

"If that 10-inch-wide, eight-pound chunk that came from the ceiling today hit you, you would be smellng angel feathers," said park service spokesman George Berklacy.

Since 1976, when the old Union Station building was renamed the National Visitor Center, train passengers have been forced to use a small, often criticized "replacement station," located in the rear of the original white granite station. Until Monday, passengers could walk through the old building on the way to the trains. They now have to walk outside in the weather more than 400 feet to reach the replacement station and the trains.

Moynihan's bill, cosponsored by senators Jennings Randolph (D-W.Va.) and Robert t. Stafford (R-Vt.), would transfer control of Union Station from the Department of Interior to the Department of Transportation, complete an uncompleted parking garage that has already cost more than $36 million and move the visitor facility to a smaller part of the station.