It isn't just Washington area roads that are getting clogged these days: Commuter rail lines are experiencing their own traffic jams.

The sound of the whistle signaling an approaching passenger train has become much less predictable since CSX Transportation Inc., which operates most of the commuter lines, acquired half of Conrail earlier this summer. The merger has meant more freight trains on the same lines that carry commuters, slowing everything down.

"It's been awful," said Mike Budzinski, a writer who commutes from Laurel to Union Station on a Maryland Rail Commuter service (MARC) train every weekday. "I've ridden on these trains for several years, on and off . . . and service was pretty good. By and large, trains were on time. But pretty much since the merger, it's been just atrocious."

The problem has hit commuters hardest along the Camden line, which takes riders from Baltimore to Union Station--passing through Laurel on the way. State transportation officials said Camden line trains arrived on time 91 percent of the time from January to May, before the merger. Since then, however, the on-time rate has dipped to 77 percent. There have been similar, though less drastic, slips in service on the Brunswick line, which takes commuters between Washington and Martinsburg, W.Va.

Virginia transportation officials said their trains also have been slowed since the merger. Virginia Railway Express (VRE) trains on the Fredericksburg line, which is owned by CSX, slipped below a 90 percent on-time rate--to 82 percent--in June, when the merger took place. VRE spokesman Matt Benka said the rate rose to 88 percent in July and 90 percent in August.

Maryland officials have been pressuring CSX to improve passenger service, which it provides for the state in exchange for permission to run its more lucrative freight operation. Maryland's U.S. senators, Paul S. Sarbanes (D) and Barbara A. Mikulski (D), wrote a letter to CSX Chairman John W. Snow last month, asking for immediate action to correct the deficiencies.

State Transportation Secretary John D. Porcari echoed their concerns yesterday and noted that Gov. Parris N. Glendening (D) has made doubling transit ridership a goal of his administration. "It is very difficult to work on doubling transit ridership when an existing service like MARC is having these kinds of delays," Porcari said.

The delays have become so common that some commuters on the platform in Laurel yesterday morning were actually surprised to see the 8 a.m. train pulling into the station right on time.

"The last few months have just been horrible," said Debbie Thomas, who rides the train to her job at a downtown trade association every day.

"You just never know whether the train is going to be on time or not," said Althea Chase, an accountant at a downtown hotel. "For me, its not so bad, because I have flexible hours. But a lot of people don't."

Yet it's not just the number of late trains that has upset commuters, but also how late they are. In their letter to Snow, Mikulski and Sarbanes cited one northbound Camden-line train that was held up for one hour and 20 minutes because of signal problems. But many other delays, they said state transportation officials told them, were caused by dispatchers giving preference to freight trains.

CSX spokesman Robert L. Gould said the company does not give preference to freight trains. He said company management acknowledges there is a timeliness problem and hopes to work out solutions with state officials. He said the company's projections on additional freight traffic created by the merger were too conservative.

"It's a matter of capacity," Gould said. "And it's in the best interest of Maryland and of CSX to work together to address this."

Commuter Budzinski does not buy Gould's assertion that freight trains are not given preference. "I've never seen another passenger train go by when my train is stopped during a delay. But I've seen freight trains go by all the time."