An 8 1/2-hour strike by machinists against the Chessie System ended yesterday afternoon, a railroad official said.

Tom Johnson said pickets left Chessie locations in West Virginia, Kentucky and Ohio about 3:30 p.m. and had agreed to talk with management.

There were no reports of picketing in Maryland.

"As far as we know it is over," Johnson said. "The pickets are going away." But Chessie officials maintained yesterday that they did not know the cause of the work stoppage. "We never found out what it was about," said Johnson.

Four locals of the International Association of Machinists struck the railroad Tuesday morning in five locations in West Virginia, Kentucky and Ohio, and other unions were honoring the picket lines, Johnson said.

A local dispute apparently triggered the strike in Baboursville and Huntingdon, W.Va., and Russell, Ky., said the Chessie Spokesman. Other district locals in Paintsville, Ky., and Columbus, Ohio joined the strike.

A spokesman for the West Virginia Coal Association, Dan Fields, said the strike against the Chessie System could have halted the movement of most of the state's coal.

Fields said that while several other railroads also haul the state's coal, the bulk of it is handled either by the Norfolk & Western Railway or the Chessie System.

A 51-day strike by the Brotherhood of Railway Clerks against the N&W railroad has resulted in layoffs of more than 11,000 West Virginia miners, Fields said. And the coal industry has already been hurt by the 111-day United Mine Workers strike that ended in March.

In Washington, industry sources said yesterday that disagreement between the Norfolk & Western railway and striking clerks have narrowed, but the major differences remain on some issues.

Negotiations between the railway clerks and the N&W were scheduled to resume in Washington today.

Both sides have imposed a news blackout on the talks but union and company sources said last weekend that a settlement was expected soon, possibly this week.

Meanwhile, an attempt to spread the N&W strike against the Chicago & North Western Transportation Co. had little effect. A C&NW spokesman said yesterday that its commuter and freight services haven't been affected substantially by a railroad clearks strike.

The strike could force the railroad to shut down its commuter lines, which serve 100,000 people a day, if many C&NW employees refused to cross picket lines.

But a spokesman said later Tuesday that "99 percent of our employees showed up for work, everything is operating normally."