Despite numerous efforts by railroads to take away labor's right to engage in secondary boycotts, they have been defeated at every turn.

Now, the CSX Transportation unit of CSX Corp. believes it may have a legal

window of opportunity that could end the secondary boycott threat.Secondary boycotts, in which a union pickets an employer that is not party to a labor dispute, were outlawed by the Taft-Hartley Act in 1947. Labor- management relations in the railroad industry, however, are governed by the Railway Labor Act, which does not ban secondary picketing.

Unions value their right to involve another carrier in a labor dispute.

Because so much rail traffic moves over the tracks of more than one road, the theory goes, other railroads will apply pressure on the struck road to settle.

Until recently, carriers routinely went to federal court and obtained a temporary restraining order against the union. By the time a full hearing might be held, or an appellate court reviewed the matter, the original strike usually had ended and the issue was moot.

Unions won a clear victory in 1989, however, when a secondary boycott dispute between the Burlington Northern Railroad Co. and the Brotherhood of Maintenance of Way Employes was upheld by the Supreme Court.

Carriers effectively lost their ability to get short-term relief from district courts.

CSX, however, believes it may have a window of opportunity that could cost unions so much money they would not be able to use their secondary boycott weapon.

When the Transportation Workers' Union struck the Pittsburgh & Lake Erie Railroad Co. on Feb. 22, 1991, it picketed CSX secondarily. CSX, which ran some of its trains over the P&LE, was seen as the benefactor keeping the struck railroad in operation.

None of CSX' employees are represented by the TWU.

Although the strike ended in less than a day, TWU said it would picket CSX facilities. Other rail unions ordered their members to stay away from work that day.

In the current dispute, which is in the discovery phase, with no trial date set, CSX is suing for financial damages, claiming the unions breached their contracts with the company.

"Most of our people never saw a picket that day because they never left their homes," says a CSX executive, who asked that he not be identified.

The company, through a spokeswoman, said it is not attacking individual employees' rights "as a matter of conscience" to respect another union's picket lines. The workers were given no choice in this case, she said.

CSX executives declined to comment, but lawyers familiar with the Railway Labor Act and the secondary boycott litigation, say the carrier obviously hopes it can use the threat of punitive financial penalties to take away the secondary boycott as an effective union weapon.

If the company wins its case, unions would be bound to use their best efforts to see that workers report to work. If workers individually chose to observe a picket line, they would be subject to disciplinary action by the carrier.

In the past, railroads have not punished workers for observing picket lines

because temporary restraining orders ended strikes quickly.

The Supreme Court, in the Burlington Northern case, took away the temporary restraining order weapon. Now, at least one railroad is escalating the conflict.

In retaliation, nine unions say they will halt all labor-management cooperative programs with CSX. Edward P. McEntee, a vice president of the International Brotherhood of Electrical Workers, and chairman of the Railway Labor Executives' Association, an umbrella labor group, called the law suit a ''blatant attempt by CSX to undermine one of rail labor's most important rights."