The controversy over operating Metro alongside railroad tracks escalated yesterday as the transit agency resumed full Red Line service and reached an agreement with CSX Corp. to alter rail operations through the corridor where two CSX trains recently derailed and cut across Metro's tracks.

Metro and CSX Corp. officials agreed to make "speed adjustments" -- beginning at 12:01 a.m. today -- in their service through the 6.5-mile shared corridor from Washington's Union Station to Silver Spring, according to a source close to the negotiations.

The officials, who met yesterday in Jacksonville, Fla., where CSX has its railroad headquarters, withheld details of their plan until announcement at the Metro board meeting today.

Metro restored Red Line service to the Takoma Park and Silver Spring stations yesterday at 12:45 p.m. after rebuilding more than 1,100 feet of inbound and outbound track that was severed Saturday night by the derailment of 12 freight cars on a 90-car CSX train.

As Metro and CSX trains started rolling past each other again, the pressure for changes increased:

CSX agreed to restrict freight, passenger and commuter trains through the corridor to 40 mph until the Federal Railroad Administration completes an audit of the track, operations and maintenance along the line. CSX's freight trains had operated under a 55 mph limit. The restriction also applies to Amtrak trains and Maryland Rail Commuter Service trains that use that track and had previously operated at up to 69 mph. The new plan between Metro and CSX is separate from the federal agreement, according to a source.

MARC and Amtrak officials said the speed restrictions could seriously delay their trains. A MARC spokesman said lengthy delays might increase highway hazard if large numbers of commuters leave the trains to drive.

A House subcommittee announced it will hold a hearing next week to examine the two recent wrecks along Metro tracks and the danger posed to communities and transit systems by freight train derailment.

CSX officials agreed to the temporary speed restriction "in the spirit of concern and mutual cooperation," said spokesman R. Lindsay Leckie. "We want to determine if there is any common thread to these two accidents alongside Metro trackage."

FRA Administrator John H. Riley, citing equipment and track problems that might have caused CSX derailments on Saturday and June 19, said the speed restrictions should reduce the chance of other accidents occurring because of similar reasons. The slower speed also would lessen the damage from any crashes that may occur caused by other factors, he said.

The June 19 derailment of 21 cars north of Fort Totten station occurred as a 134-car CSX train ran southbound at 42 mph. The Saturday wreck occurred as a train ran southbound at 55 mph.

CSX attributed the June accident to a broken center support beam in a refrigerator car; two federal investigations have not determined the official cause. FRA and National Transportation Safety Board experts investigating the Saturday crash are focusing on a worn track switch and two worn freight car wheels as possible causes.

High speeds rarely cause freight train derailments, but can increase pressure on weak equipment or track, Riley said.

The verbal agreement between CSX and FRA, reached before midnight Tuesday, caused confusion for Amtrak and MARC yesterday.

FRA and CSX said the lower speed limit for CSX, Amtrak and MARC operations over the 54-mile line from Harpers Ferry, W.Va., to a tower near the Rhode Island Avenue station.

But MARC and Amtrak, saying they were following CSX instructions, observed the limit only over the 6.5 miles between Silver Spring and the Rhode Island station. MARC reported no delays, and Amtrak reported delays of about two minutes over the line.

But both said they will suffer serious delays if they have to slow their trains over the 54-mile stretch. "If it applies to us all the way to Harpers Ferry, we've got a major problem," said MARC spokesman Bob Shreeve.

The lower speed limit could increase highway hazards by driving rail commuters onto the road, Shreeve said. The new limit would almost double travel time of MARC's 12 rush-hour trains, which carry about 3,200 riders a day, he said.

"This train system represents one lane of rush-hour traffic . . . if you put them all on I-270, where do they go?" Shreeve said. "How many people are we going to kill while {speed limit} is going on?" he asked.

Maryland Del. Peter Franchot (D-Montgomery County), who has asked CSX to operate trains while Metro is not running, criticized Metro for restoring service while CSX trains run in the corridor.