A TEXAS NURSE named Kindra Bryan, who had gone to Mozambique to do relief work, was abducted by rebels in May. Sen. Jesse Helms, a champion of Renamo, the rebel group, took the occasion to press his campaign to induce the State Department to take up the Renamo cause. Call its local representative, Howard professor Luis Serapiao, Sen. Helms told a State witness on June 24, and ''you'll get your hostage released in five minutes.'' Three days later, the department's Mozambique desk officer reached Mr. Serapiao. Nearly three weeks later, Kindra Bryan remains a Renamo prisoner.

More is at stake than Sen. Helms' embarrassment at the hands of a group that enjoys his political favor. For almost a year, he has been conducting an ''abduction'' of another sort, holding up confirmation of the veteran diplomat Melissa Wells as President Reagan's ambassador to Mozambique. His purpose is to defy the official policy of attempting to pry Mozambique from its earlier embrace of Marxist philosophy and Soviet alliance. For Mr. Helms it is enough that Renamo is anticommunist. ''Until you treat all freedom fighters in the world the same,'' he told the State Department, ''you're going to have problems with me.''

Since the U.S. government aids Jonas Savimbi's UNITA in Angola, the question is asked: why not also aid Renamo in Mozambique? It's a fair point. In fact, it's a mistake to go with the guerrillas, and thereby become a partner of South Africa, in either place. In Angola, the presence of Cuban troops defending the government eventually overcame the administration's initial unwillingness to make common cause with Pretoria. In Mozambique, the absence of a Cuban factor has let President Reagan keep his distance from Renamo. But his policy, though firmly supported in the State Department, is under pressure from conservative elements not just in Congress but also in other executive departments. They are presenting the recent working-level State contact with Renamo's man in Washington as a harbinger of sweeping policy change.

Washington has worked to offer Mozambique more security and more development than it could expect from Moscow. The results are measurable and constitute one of the few successes for the policy of ''constructive engagement.'' Jesse Helms would throw this away by having the United States switch horses and back his favorite gang of kidnappers.