The Carter administration, fearful that the Nicaragua civil war will lead to an eventual takeover by radical guerrillas, is considering a new attempt to induce President Anastasio Somoza to surrender power to his country's political moderates.

Authoritative sources said yesterday that U.S. policy, limited until now by administration-imposed strictures against intervention, is shifting toward pressuring Somoza more overtly to step aside.

These sources stressed that no decisions have been made yet about the specific tactics to be used. They also added that whatever course is followed will stop far short of such possibilities an interposing U.S. Troops in the fighting between Somoza's National Guard and the guerrillas of the leftist Sandinista National Front.

But, the sources said, the latest outbreak of bloody civil war - the second since last September - has convinced the administration that the Somoza family's 46-year control of Nicaragua is collapsing and that, unless urgent steps are taken to bring a moderate solution, a Sandinista capture of power seems inevitable.

The administration, the sources continued, does not foresee an immediate crumbling of the Somoza regime. Instead U.S. intelligence sources estimate that the National Guard retains sufficient military superiority to put down the latest Sandinistra challenge and force the guerrillas back across the border to their bases in neighboring Costa Rica.

Still, the sources added, the ability of the Guerillas to regroup and mount new large-scale offensives, coupled with the support they enjoy from the Nicaraguan masses, has made clear that Somoza is becoming increasingly isolated. As a result, U.S. officials now believe it is only a matter of weeks, or at most months, before the pressures building against him become too strong to withstand.

As a first step toward finding a solution before that happens, the State Department sent William G. Bowdler, its director of research and intelligence, to Latin American over the weekend to consult with regional governments on possible joint approaches in which the United States might participate.

Bowdler's full itinerary and the extent of his conversations were not immediately known. However, department officials did reveal that they include talks in Costa Rica with representatives of the Andean Pact countries, which have called jointly for an urgent effort to end the Nicaraguan fighting.

Since last September, U.S. policy makers openly have taken the position that Somoza should give up the presidency and allow his moderate opposition from the Nicaraguan business and professional classes to prepare the country for a transition to democratic processes.

But, in pursuing this goal, U.S. officials have been required to operate within guidelines stressing President Carterhs pledge not to intervene openly or covertly in the internal affairs of other countries.

As a result, the administration's initiatives have been limited to relatively mild pressures such as cuts in aid and the U.S. embasssy staff, and to an unsucessful mediation effort, undertaken by Bowdler and two Latin American officials under the auspices of the Organization of American States.

When these tactics proved insufficient to dislodge Somoza, the effort was put on the back burner - primarily because of the administration's deep-seated aversion to foreign intervention and, to a lesser extent, because of Carter's more immediate concern with getting the enabling legislation for the Panama Canal treaties through the House.

The canal legislation faces such serious opposition that the administration was forced to ask the House leadership to postpone a vote on it that had been scheduled for yesterday. The opposition stems in part from the success of Somoza's congressional supporters in portraying the bitterly anti Somoza Panamanian government as a backer and supplier of arms to the Sandinistas. House Speaker Thomas P. O'Neill Jr. (D-Mass.) said yesterday the canal bill may come up next week.

When Panamanian President Aristides Royo visited here last month. Carter reportedly told him that, because of the link, the administration could not do anything about Nicara gua until the canal treaties had cleared the House.

U.S. sources, while conceding that had been an inhibiting factor, said yesterday that Carter was speaking at a time when the internal Nicaragua situation was quiet. Since then, the sources continued, the renewed fighting there has changed the equation so drastically that the administration can't avoid confronting the Nicaragua situation even if it means a risk of trouble for the canal treaties.

The administration's first considerations, the sources said, must be the continuing blooshed and suffering of the Nicaraguan people and the possibility of a takeover by forces that include at least some Marxist, pro Cuban elements.

In addition, they added, the administration must take into account growing Latin American fears that the conflict could spill over into other countries and the tendency of the region's democratic governments to regard Washington's handling of Somoza as a test of the U.S. commitment to hemispheric democracy.

"The United States has to do something," one source said. "We'd prefer not to be out front. But, given the intense emotion the situation is generating throughout Latin America, we can't be the last to act."

In exploring its various options, the sources said, the United States will seek to act in concert with other hemisphere countries, preferably in an effort like the mediation proposal made by the Andean Pact. If that fails, they added, Washington then will have to consider tougher steps such as associating with efforts to impose sanctions against the Somoza regime.

A call for even stronger measures was made yesterday by Sen. Edward Zorinsky (D-Neb.), chairman of the Senate's western hemisphere affairs subcommittee. He said the United Staes must use its influence "diplomatically if possible, military if necessry . . . to get rid of Somoza."