Secretary of State Alexander M. Haig Jr. will make a one-day visit to Romania late next week, his first trip to Eastern Europe since the onset of martial law in Poland, the State Department announced yesterday.

Haig's journey to Bucharest, a last-minute addition to a planned trip next week to Spain, Portugal and Morocco, was undertaken after a personal invitation in recent days from Romanian President Nicolae Ceausescu, according to State Department officials.

The visit to Romania will give Haig an opportunity to dramatize the U.S. policy of differentiation between the Soviet Union and its Eastern European allies. Romania has been one of the most politically independent of the Warsaw Pact nations for many years, maintaining relatively warm political and economic relations with the United States and departing to some extent from stands adopted by the Soviet Union and other Eastern European countries.

Last fall Ceausescu called for the withdrawal of Soviet nuclear missiles from Europe as well a halt to the planned U.S. deployment of medium-range nuclear missiles there, a more balanced stand than other Warsaw Pact nations. Romania also has called for an early end to martial law in Poland and a return to dialogue among the internal forces there, according to U.S. sources.

At the same time, however, Romania is reported to be increasingly dependent on the Soviet Union for its energy supplies and thus more vulnerable than before to pressures from Moscow.

This is also a delicate moment in Romania's economic relations with the West, because of Romania's inability to make the large payments coming due on $11.4 billion in outstanding debts to European and American banks. Last week in Bucharest a group of the bankers reportedly agreed in principle to give Romania more time to repay.

According to official sources, one of the conditions of the private banks is that Romania work out a rescheduling agreement with western governments, to which smaller sums are owed. Romania is reported to have contacted the French government about convening a meeting of western governmental creditors, including the United States, which is owed $275 million in official debt.

Unlike Poland, where the United States has suspended official debt rescheduling negotiations due to the martial law, Washington is expected to go along with Romania's desire for debt renegotiations, assuming that normal economic criteria are met.