Like a stone thrown into the Mediterranean, an accord of union signed Aug. 13 by the leaders of Libya and Morocco stirred a few ripples but has since been largely ignored by a world concerned with apparently more urgent matters - including the possibility that a Libyan ship was the source of mines in the Red Sea and Gulf of Suez.
But this new link between Morocco's King Hassan II and Libyan leader Muammar Qaddafi is a setback for Reagan administration policy in North Africa and the Middle East. If lasting - and it must be noted that previous ''unions'' announced by Colonel Qaddafi with Egypt, Syria, Tunisia, Chad, and the Sudan never became effective - the consequences could be serious.
Under President Reagan the United States has built a relationship with Morocco that amounts to an alliance. The US has furnished Morocco both economic and military aid and in turn has been given the right to use facilities in that country as transit bases for the Rapid Deployment Force. American military advisers and technology have played a major role in training Moroccan troops involved in an eight-year conflict with Polisario rebels in the Western Sahara.
With the loss of its bases in Iran, with uncertainty about the attitude of Spain's socialist government on continued American use of bases there, and with Egypt's need not to be too closely tied to the US, the availability of the Moroccan facilities has been considered very important, if not vital.
In the wake of announcement of the union, US officials - who were surprised at the timing if not the pact itself - are reserving comment, but they are said to have been in touch with officials in Rabat.
A pause for pro forma ratification votes in both countries in early September provides time for the US and other nations to consider their options.
If the Libya-Morocco union is disturbing news in Washington, it must be equally unsettling for members of the Organization of African Unity who have been trying to get Hassan's government to negotiate with the Polisario forces.
Relations between the Arab nations of North Africa shift like the Sahara's sands, and past major-power agreements with those nations have had the instability of houses built on sand. Algeria, whose 700-mile girth splits the new union, is at odds with Morocco over the Western Sahara matter and would like King Hassan to negotiate with the Polisario.
In July of 1983, Libya's Qaddafi visited Morocco for the first time in 14 years and got Hassan to agree to a joint communique resolving to settle the Sahara conflict through the OAU. Now it appears that Hassan may have won the Libyan's support for continuation of the struggle in Western Sahara in exchange for ''union'' and perhaps support of Qaddafi's disputed claims in Chad.
It may be too much to hope that the new Libyan initiative, whatever Qaddafi's motives, might be the catalyst for a settlement of the Western Sahara conflict. But stranger things have happened in the area.
Meanwhile, it is difficult to see how the presence of US tanks and other military supplies in Morocco and the right to use transit bases in that country can exist side by side with a Libyan-Moroccan union.
It's a delicate diplomatic challenge for a Republican administration that has had few successes in that part of the world and is about to enter an election campaign in which international relations may well be a major issue.