A strike involving a Maine railroad came south yesterday and prompted 360 railroad workers to walk off their jobs at the Potomac Yard, a major East Coast rail facility near National Airport.

The workers left the yard in Alexandria after striking employes of the Maine Central Railroad established a picket line there. Contract talks between the union and the railroad, being held in Washington, had collapsed Thursday night.

Despite the sudden walkout, spokesmen for the freight yard and its owner, the Richmond, Fredericksburg & Potomac Railroad, said there was no disruption of service because supervisory personnel took over for the employes.

"It is not crippling us and we do not expect a curtailment of service," said RF&P Senior Vice President Sidney Johnson.

He said the strike would not affect Amtrak schedules because passenger trains run on parallel tracks outside the yard.

The RF&P sought a temporary injunction against the pickets in federal court in Alexandria yesterday afternoon, arguing that the strike is not against RF&P or any of the other five railroads that are tenants of the yard. District Judge Albert V. Bryan Jr. rejected the request, saying, "I think the definition of a labor dispute is broad enough" to allow the pickets to remain.

The 305-acre yard, a nerve center for rail operations on the Eastern seaboard, is the latest target of the month-old strike by a Maine chapter of the International Brotherhood of Maintenance of Way Employees. The union's members lay and maintain tracks.

The strike, which began over job security and severance benefits, has disrupted freight rail service in New England, New York and Pennsylvania, as well as commuter rail service in the Boston area, as members of the 75,000-member union honored picket lines in those areas.

The strike involves 112 employes of the Maine Central Railroad, one of three railroad companies owned by the Maine-based Guilford Transportation Industries. Guilford also owns the Delaware & Hudson Railroad, which has the right to use Conrail's tracks into the Potomac Yard and which uses the yard as its southern terminus.

The union struck the Maine Central on March 3, and both parties had been negotiating in Washington under the auspices of the National Mediation Board, which oversees railroad and airline disputes.

A spokesman for the National Mediation Board said no date has been set for a resumption of talks and no decision has been made by the agency's director, Walter Wallace, on whether to ask President Reagan to convene a special Presidential Emergency Board. Such a board, independent from the mediation board, could order the employes back to work for 60 days while new efforts are made to resolve the impasse.