Thousands of cheering Nicaraguans lined the streets this evening to welcome home newly elevated Roman Catholic Cardinal Miguel Obando y Bravo in a gathering marked by one of the largest showings of antigovernment feeling since the Sandinistas came to power nearly six years ago.

Obando returned from his investiture as cardinal less than a day after the leftist Sandinista government, in a move likely to raise tensions further with the United States, revived threats to acquire jet warplanes in response to the U.S. Congress' approval of funds for Nicaraguan antigovernment guerrillas.

Obando, the most prominent domestic critic of the Sandinistas, flew in from Miami to be greeted by the largest demonstration on behalf of anyone outside the government since Pope John Paul II visited here in the spring of 1983.

The church said beforehand that the welcome would be a religious rather than a political event, but the crowd's feelings were unmistakable. It hooted and jeered at a truckload of Sandinista police, and the normally conspicuous red and black Sandinista flag was replaced for the evening by Nicaragua's blue and white national colors and by yellow and white banners of the papacy.

The arrival and procession generally were peaceful, but police used fire hoses to drive about 200 persons out of an airport parking lot where they were awaiting the cardinal. That group, and others in the crowd, responded by pelting the police with rocks.

Obando waved from the back of a pickup truck that moved painfully slowly through the crowd thronging the road from Sandino Airport into the capital. A young man with a megaphone walked ahead and shouted to the crowd, "Do you want communism?" The answer came back: "No!" He asked again, "Do you want Christianity?" The answer: "Yes!"

The demonstration appeared to confirm predictions by some diplomats and Nicaraguan politicians that Obando's elevation on May 25 from archbishop to cardinal would bolster his prestige at home and perhaps increase his impact as an opposition figure. The church has played a leading role in opposing the unpopular military draft and has criticized the government for having "totalitarian tendencies."

"This crowd means that the cardinal has his people too, people who are against the government," a 46-year-old typographer said.

While a few police and Army vehicles drove down the procession route, the Sandinista police presence was minimal. An enthusiastic account of the cardinal's arrival and of the procession were broadcast live nationwide on Catholic Radio.

In a separate development, President Daniel Ortega went on nationwide television yesterday evening to announce that the government was withdrawing its pledge made last Feb. 27 not to add new types of weapons, and specifically advanced warplanes, to its arsenal. A communique said that this decision was in reply to Wednesday's U.S. congressional vote in favor of funds for the guerrillas.

A senior Foreign Ministry official indicated today that Nicaragua's arms suppliers would be willing to supply such aircraft if the rebels, also known as contras, significantly stepped up actions against the Sandinista government.

Nicaragua's military backers, principally the Soviet Union, have been reluctant so far to deliver combat planes here, apparently for fear of provoking the United States. "This is going to depend on the level of aggression. If the aggression increases, then I think other countries will be in accord that Nicaragua needs the means to defend itself," Saul Arana, director of the Foreign Ministry's North America Department, said in an interview.

In Washington, a senior State Department official said Ortega's announcement "doesn't mean much of anything since we didn't take (the arms purchase moratorium) seriously when he imposed it," staff writer Joanne Omang reported. The official said the moratorium "happened to coincide neatly" with a break in scheduled arms shipments and with the exceeding of Nicaragua's capacity to absorb more arms.

"They were looking for some way to respond to the vote (in Congress) and seized on this," he said, adding that he did not expect Nicaragua to buy advanced jets. "That still would be a pretty dumb thing for them to do, and they know it."

Nicaragua had said before February that it was seeking jet warplanes such as Soviet-made MiG21s or Czechoslovak-made L39s to bolster its minuscule Air Force. U.S. officials have said that the United States would attack such aircraft if they were delivered here, asserting that Nicaragua otherwise would gain an unacceptable military advantage over its neighbors.

In a "unilateral pledge" in February, Nicaragua said it would not continue to seek the planes, which was interpreted as part of an effort to persuade Congress to withhold funds from the contras.

The government's shift yesterday did not necessarily mean that Nicaragua would succeed in acquiring such warplanes, given Moscow's unwillingness so far to deliver them, according to diplomats and other political observers here. They said that the change in Nicaragua's public position was best understood as a publicity move to show Congress that support for the contras had counterproductive results.

"I don't think they're going to get" the planes, a diplomat here said today. "These are things you put on the bargaining table and then take off. They're saying, 'This is your response, Congress, for being gutless and bending to Reagan's will.' "

The government also said yesterday that it was taking back its decision in February to send home 100 Cuban advisers, whose presence has been criticized by the United States.

The original move was considered mainly symbolic, as the United States estimates that there are about 2,500 Cuban military and security advisers here in addition to a much larger number of medical and technical personnel. Nicaragua says there are fewer than 800 Cuban military and security advisers here.

The government here seemed to have been shocked by the congressional vote, which ended a period of nearly a year during which the contras were cut off from U.S. funds.