MANAGUA, NICARAGUA, NOV. 21 -- Nicaragua's Cardinal Miguel Obando y Bravo, displaying considerable political skill, moved carefully this week to make sure he will have substantial influence as intermediary between the leftist government and U.S.-backed rebels. In so doing, the 61-year-old Roman Catholic primate is emerging as the pivotal figure in the peace process here.

The cardinal's deft actions have inspired hope among diplomats in Managua that Obando will try to guide and expand the cease-fire talks to forge a political settlement in Nicaragua.

Obando's role has become crucial since the Sandinista government asked him to serve as president of a four-man National Reconciliation Commission, which monitors progress in Nicaragua of a regional peace plan, as well as intermediary in the cease-fire talks.

Without the cardinal, prospects for constructive talks between the conservative contras and the Marxist-leaning Sandinistas seemed poor after seven years of a punishing war that has taken about 45,000 Nicaraguan lives.

Before the peace accord was signed Aug. 7 in Guatemala, Obando was one of the Sandinistas' sternest critics. The rebels, known as contras, have long claimed Obando as their spiritual leader and insisted that he mediate.

The cardinal came under the spotlight last week when he followed President Daniel Ortega to Washington to receive, in a meeting at the Vatican mission with Ortega and House Speaker Jim Wright (D-Tex.), the government's first 11-point cease-fire proposal.

However, the cardinal has yet to accept formally the job of intermediary. Before going to Washington he conferred with key members of Nicaragua's eight-man bishops' conference, obtaining their support to "probe" the possibilities of the role but not to accept it.

Since his return, Obando has demanded letters from both the government and the contras ratifying and describing his mediation. Once he has the letters, the cardinal said yesterday, he will go back to the bishops for their final approval. He has already received votes of confidence from U.S. bishops, from his own National Reconciliation Commission and from Wright and Secretary of State George P. Shultz.

Obando "has a keen political sense. He is utterly able to master his own feelings and remain serene under attack. This man is going to be surprising -- even dangerous -- for every side in this negotiation," said one top western diplomat who knows the cardinal.

Contra leader Alfredo Cesar said in a telephone interview from Costa Rica that the Nicaraguan Resistance, the broad contra alliance, has composed its letter but has not yet been able to deliver it to the cardinal.

Thursday night Ortega paid a visit to the cardinal at the Managua archdiocese to deliver his letter. In it Ortega encourages the cardinal to make "suggestions and recommendations" as intermediary.

Ortega also says the peace pact calls for the contras to use the cease-fire period to disarm and return to civilian life in Nicaragua. He tells Obando the "essential aspect" of his role will be to work out whatever guarantees the contras will require to make the transition to open participation in politics here.

Contra leaders roundly rejected Ortega's first cease-fire proposal, which calls for them to fall back into fixed zones to begin to disarm Dec. 5. Cesar called it a "formula for our surrender." Obando said he delivered the document to contra leaders in Miami Nov. 13.

"That was just Ortega clowning around before the cameras in Washington for propaganda purposes," said Alfonso Robelo, another Nicaraguan Resistance director, by phone from Costa Rica. Robelo said the contras have readied their own cease-fire position but don't want to make it public.

Instead, they prefer to submit their proposal to the cardinal in a closed, face-to-face meeting somewhere in Central America once he agrees to serve as go-between. So, while they had planned to proceed quickly, the contras now have to wait for Obando to formalize his role, which he may do sometime this week.

Contra leaders said they want their forces in Nicaragua to be allowed to remain armed in place, to be able to receive food and other nonmilitary supplies and to communicate freely with their commanders. They may demand that the government recognize their control over some territory.

Meanwhile, in conversations with diplomats and others, Obando has sought to distance himself from his close identification with the opposition, stressing that he feels he must represent all Nicaraguans in the negotiations.

He has also emphasized that he is proceeding in close consultation with the Vatican. For the past year, Rome's policy toward Nicaragua has been to accept the Sandinista government as an established power and to press it for more religious freedom and a political solution to the war.