President Reagan's decision to nominate John Holdridge ambassador to Indonesia may solve one problem for the administration but create another, by opening up one of the most controversial policy-making jobs at the State Department, assistant secretary of state for East Asian affairs, the job that Holdridge leaves.

Reagan announced his surprise decision to nominate Holdridge Tuesday night, closing out months of awkward indecision over how to fill the ambassadorship to Indonesia.

But the next step, nominating a Holdridge successor, may set off a whole new debate over administration policy in the Far East, and particularly toward Taiwan and China.

Holdridge's own appointment as assistant secretary was held up for five months in a dispute between conservative senators, led by Jesse Helms (R-N.C.) and the new administration over the political coloration of key appointees in general and policy toward Taiwan in particular.

There were no indications yesterday who Secretary of State George P. Shultz might have in mind to replace Holdridge but whoever it is likely will face tough questioning on the interpretation of the August U.S.-China communique on Taiwan.

Under the communique, the United States said it would limit arms sales to Taiwan to the quantitative and qualitative levels of recent years and even reduce sales gradually.

China, in turn, stated its "fundamental" policy of seeking a peaceful reunification with Taiwan.

Taiwan supporters in Congress have attacked the agreement as a violation of the Taiwan Relations Act.

Apparently in response, Chinese officials in recent weeks have resumed sharp attacks against U.S.-Taiwan relations.

"It's clear that whoever is named will face closer questioning on China than Shultz did at his nomination hearings, but I think we will be able to weather it," one knowledgeable official said, acknowledging that the process is likely to cause some further uneasiness in Peking.

Holdridge is expected to have an easier time in his ambassadorial nomination than he did the last time he had to go before Congress, especially given the presidential prestige now attached to what normally would be a routine embassy selection.

Reagan announced the selection at a state dinner Tuesday night for President and Mrs. Suharto after more than a year during which the administration could not come up with a name that would meet the approval of both interested domestic groups and the Indonesians.

Holdridge's selection was a closely held secret and even his closest associates said he had not given the slightest inkling a change was in the offing.

Holdridge is known as a policy-maker who traditionally has kept his own very close counsel.

Given that Congress will meet in a lame-duck session for only about three weeks during December, and primarily to deal with pending budget matters, it could be February or later before hearings could be held on a new assistant secretary for East Asia.

Holdridge will continue to serve in his present post until confirmed to Jakarta, a State Department spokesman said yesterday.

Shultz also has yet to name a replacement for James L. Buckley as State Department counselor. Buckley has been named to head the Munich-based Radio Free Europe and Radio Liberty, U.S. funded stations which broadcast to Eastern Europe and the Soviet Union respectively.

Not only was the forum for the announcement of Holdridge's appointment unusual, but it is rare to tap the assistant secretary ranks to fill ambassadorships except when a change in administration is imminent or has taken place.

Holdridge's appointment appears to reflect the extraordinary sensitivities which had come to surround the Indonesian case after almost a year of delays.

Holdridge previously has served in Peking, as ambassador to Singapore, on the National Security Council under Henry A. Kissinger and as National Intelligence Officer for East Asia, the top-ranking official in an area within the U.S. intelligence community.