For more than eight months, the Senate has been manhandling the nomination of a career foreign service officer, Melissa Foelsch Wells, to be the American ambassador to Mozambique. Wells is hardly the first (and will certainly not be the last) ambassador-designate to be caught up in a foreign policy power play. Mozambique, a faraway, famine-stricken former Portuguese colony on the southeast coast of Africa, scarcely qualifies as a top-priority U.S. security concern.

But even as a microcosmic case study, this one has macro-implications that only begin with the all-too-familiar mean-minded mischief-making of North Carolina's Sen. Jesse Helms or the ideological hooliganism of the far right.

The charge against Wells (as is usually the case) has nothing to do with her credentials or her competence. Her problem, as one State Department official puts it, is that she is ''100 percent guilty of supporting the Reagan administration's position'' on Mozambique. It is the Reagan policy that her critics (mostly Republicans) cannot abide. And the reason for this is that over the past four years the Reagan administration has been sensibly and successfully standing the ''freedom fighting'' fixation of the Reagan Doctrine on its head in Mozambique.

Undeniably, when the ''anti-imperialist'' revolutionaries in Mozambique broke away from Belgium's colonial rule, they turned to Marxism-Leninism for inspiration and to the Soviets for military aid against RENAMO, a ragtag rebel movement of the most dubious origins. RENAMO was created by the white supremacist government of Rhodesia in an effort to blunt Mozambique's support for the liberation movements that eventually brought independence to what is now Zimbabwe. For its legitimacy, it now relies on the sponsorship of South Africa.

Also undeniably, Mozambique's young government wrecked the country's economy with its Marxist doctrines and fell afoul of the Carter administration's human-rights policies by its repressive ways. But in 1983, President Samora Machel made a conscious decision to loosen the Moscow connection, introduce economic and social reforms, and reach out to the West.

The results fall well short of a break with Moscow or Marx. But they were sufficiently impressive to bring an invitation to the White House for Machel from Ronald Reagan in 1985. After Machel died in a plane crash last year, the trend continued under his successor, Joaiquim Chissano. His recent call on Britain's impeccably conservative Prime Minister Margaret Thatcher won him a doubling of British aid. America's most important Western allies, as well as strategically located black African states, support the Mozambique government and the Reagan administration's policy. Black African states bordering on South Africa depend on Mozambique's road, rail and pipeline links to Indian Ocean ports.

But that's not enough for Helms & Co. They would use Melissa Wells as a bludgeon to reverse the Reagan policy and put the United States on RENAMO's side of the struggle. In his distinctive, low-down, high-handed way, Helms did not even show up for Wells' brief confirmation hearings. He voted by proxy against her when the nomination was overwhelmingly approved by the committee. Whereupon, he bully-ragged her with an unprecedented 246 picky-picky, tendentious and largely irrelevant written questions.

Up to a point, this is vintage Helms. What's new is that he has rallied roughly twice the dozen or so archconservative Senate colleagues he can usually count on when he sets out to make life miserable for Reagan appointees. A modicum of respectability has been added by the inclusion of Minority Leader Robert Dole. As majority leader, Dole used to insist in these matters on a reasonably prompt test -- on the merits.

But Dole now is running for president. RENAMO has a lobbyist papering Congress with geopolitical junk mail. Clearly, right-thinking about RENAMO will be made into a litmus test when it comes to raising money from conservative sources in next year's campaign.

A preliminary, procedural vote suggests Wells would win 56 to 28 if the question were put to a decisive test. But Helms and his wrecking crew are threatening a filibuster, and Democratic Majority Leader Robert Byrd wisely wants to have the extra votes that would be needed to invoke cloture and bring this squalid business to a close.

Secretary of State George Shultz has let it be known that he and the president will hang tough. That's their duty -- and their right. The Senate's duty is to demonstrate that it is worthy of its right to a reasonable role in the conduct of foreign policy. That means not permitting its power and its procedures to be subjected to such shabby abuse.