The empty chair in Jakarta

America has no ambassador to Indonesia.

Compared to what could be said about the critical state of US relations with Japan, Western Europe, and the USSR, the complaint sounds trivial.

It is not. Indonesia is the fifth most populated country in the world; a major source of minerals, oil, and natural gas; and the archipelagic turnstile between the Indian and Pacific Oceans.

Over the last 15 years, with Western help, Indonesia's President Suharto has consolidated his anticommunist, procapitalist regime. Western-trained technocrats in his cabinets, the so-called ''Berkeley Mafia,'' have encouraged a rapid expansion of the country's economy. In the Association of Southeast Asian Nations (ASEAN), Suharto has committed Indonesia to cooperate with Malaysia, the Philippines, Singapore, and Thailand, whose leaders are, like him, close to the United States and suspicious of China and the USSR.

In contrast, in Indochina over the same decade and a half, Washington has seen its client regime in Saigon overwhelmed by Hanoi, Hanoi aligned with Moscow , and Moscow enabled to project military force throughout Southeast Asia from Vietnamese bases. By strengthening the hand of noncommunist Southeast Asia, Suharto has offset this ''loss'' of Indochina and helped Washington to counterbalance Soviet influence in the region.

In the light of these political debts to Jakarta, and Jakarta's considerable material debts to Washington, why has the US ambassadorship to Indonesia been vacant for nearly a year?

The answer makes neither government look good. Bureaucratic inertia and factional infighting in the Reagan administration, along with extreme sensitivity if not actual prejudice on the part of Jakarta, reinforced each other to sabotage one nominee for the position and, since then, to delay his replacement.

Jakarta has at least tried to wipe the slate clean. A new and unusually able Indonesian ambassador has arrived in the US, and Indonesian officials have promised to accept Washington's next appointee, whoever he or she may be. Meanwhile, plans proceed for Suharto to come to the US in October - only his second state visit since he became Indonesia's president more than 14 years ago.

But an American envoy has still not been named. Instead, a new issue has arisen to delay action on the American side: Should the next US ambassador be a career foreign service officer, appointed on professional grounds, or a Republican loyalist, selected on political ones?

Since Indonesia became independent after World War II, eight American envoys have been stationed there. All of them were career diplomats. Many had served in Indonesia previously. Most knew at least something of the national language; a few were versatile.

Some of these foreign service officers performed more ably than others. But all of them were better equipped to speak for the US in Indonesia, and to interpret Indonesia to Americans, than most political appointees would have been. Noncareer ambassadors of the high caliber of, say, Edwin Reischauer and Mike Mansfield in Japan are exceptions, not the rule.

Economically, Indonesia has done better than Iran, Nigeria, or Mexico - other petroleum-exporting countries with large populations. At the end of 1981, when Mexico's foreign-currency borrowings exceeded its holding by $43.2 billion, Indonesia enjoyed a net excess of $1.5 billion in deposits over obligations.

But, like Mexico, Indonesia has suffered from falling world demand for oil, and Suharto's government remains vulnerable to the ''Mexican syndrome'' of bureaucratic corruption, domestic inequality, foreign debt, and monetary disarray. A gradual devaluation of the rupiah has already begun.

In months to come, economic nationalism will remain attractive to Indonesia's rulers, partly as a means of outflanking domestic criticism that Western and Japanese investors have been treated too generously. Although Suharto's reelection next March is a foregone conclusion, the political temperature in Indonesia will rise between now and then, especially if the economy worsens.

In light of the potential for destabilization, the Reagan administration would do well to send to Jakarta an envoy who is professionally equipped - to represent the US, to understand Indonesia, and thus to benefit both countries.

It is time to fill America's empty chair in Jakarta.