The president can fairly claim to have renewed the mandate for the foreign policy of his past four years. He drew most voters, including many who supported Walter Mondale, to the idea of building strength and conveying American will. But these are not in themselves ends of policy. The large question that hovers over his second term is the use to which American power and resolve should be put: to confirm an edge over Soviet power and what are regarded as its revolutionary offshoots or to work toward some sort of strategic and political balance, ragged as it might be. The electorate has spoken, but it has not said precisely whether he should hang tough or translate his first-term investments in strength into second-term diplomatic accords. That crucial choice remains his.

Persons representing both tendencies serve him. The tensions between them are deep and often tinged by personal bitterness. For the most part the president has remained blithely above the fray, maintaining, as he did yesterday, there is "no conflict." Whether he believes this is uncertain. What is certain is that moderate tendencies -- of the sort that earlier brought Mr. Reagan himself to end the gas pipeline fight and also to deal with the People's Republic of China -- are not going to prevail without his firm, clear intervention.

Personnel choices at the Cabinet and sub-Cabinet levels will be the first signal. Mr. Reagan is notoriously averse to cracking down on people, but unless he changes key members of the team that brought him to the impasse within his government or at least asserts his authority and intentions, the odds are against delivery on his promise of an improved relationship with Moscow, including an arms control accord.

Meanwhile, there may be an important new major player if Jesse Helms, the senior Republican, decides to replace the defeated Charles Percy as chairman of the Senate Foreign Relations Committee. Sen. Helms, personifying the unreconstructed right made heady by the results on Tuesday, makes administration hardliners look wobbly. He showed his muscle and style during the campaign when 20 or so Reagan ambassadorial appointees in effect delivered part of their political loyalty to him. Sen. Helms has used the foreign aid bill, the committee's chief annual policy vehicle, for harassment, without ever voting for a final bill.

Committee arithmetic will deny Mr. Helms, if he becomes chairman, sure majorities and may cement a working coalition of Democrats and moderate Republicans against him. But it will be fascinating to see if he will put aside his familiar guerrilla tactics and assume some of the duties -- in appointments, legislation, treaties -- normally falling upon a committee charman of the president's party. Fascinating and important: more obstructionism is the last thing Mr. Reagan needs.