Three members of a British television crew were abducted here this afternoon, but were reported found unharmed early this evening in a suburb about 30 miles north of the capital.

The abduction by armed plainclothesmen of the crew from Thames Television was the second such incident involving foreign journalists in two days amid a rising climate of hostility toward American and British reporters covering the Falklands crisis here. In both cases, the journalists have said they believed Argentine security forces were involved.

In another development, Argentine police today arrested a reporter for Newsweek magazine, Holger Jensen, on charges of violating the military censorship law. Diplomatic sources said they had been told Jensen would be expelled from Argentina tonight.

Foreign Ministry and Interior Ministry officials deplored the abductions, which they acknowledged may prove damaging to international opinion of their cause in the dispute with Britain over the islands.

"Here we are trying to do good public relations and someone comes along and does this," said Gustavo Figueroa, the chief of Cabinet in the Foreign Ministry. He said the ministry had asked the Interior Ministry to intervene directly in the case.

Thames Television producer Norman Fenton, who narrowly missed being abducted, said that Interior Minister Alfredo Saint Jean had sent his personal car and chauffeur to pick up the three men after they were located and return them to the hotel.

"Saint Jean invited us to dinner, but I think I am going to wait and see how our people feel," Fenton said as he waited for the crew to be returned.

Today's incident followed the seizure yesterday of a U.S. television journalist and two members of his crew by unidentified men. The reporter, Christopher Jones of New York's Metromedia Channel Five, was left naked on a street corner last night after being driven around by his captors for more than two hours. The crew members, who were abducted separately, were released after their equipment had been stolen.

According to Thames producer Fenton, the three were seized around 2 p.m. today as they left the Foreign Ministry, where they had been seeking an interview with Argentine Foreign Minister Nicanor Costa Mendez. Driving down a one-way street, they were cut off by a blue Ford Falcon, said Fenton, who also was in the car.

Fenton said he jumped out immediately and ran to a nearby park. From there, he said, he saw one of the three plainclothesmen in the Falcon approach the television car, open its back door and say in English, "Come this way, please."

He said the men forced one of the crew to get into the Falcon, then both the Falcon and the television car, with the two other crew members and the driver they had hired, drove off.

"It was a military operation," Fenton said. "These were professionals, no doubt about it." Other journalists said they had seen the blue Falcon near the Foreign Ministry for several days.

The driver of the Thames Television vehicle, Hugo de Lucca, was later released by the abductors. He told reporters that the men, carrying .45-caliber pistols, had forced him to follow them about 30 miles along a road leading out of Buenos Aires. They then stopped, took the two men out of the television car and told de Lucca to leave, he said.

De Lucca said that the men told him they were thieves and that they wanted to steal the camera equipment of the television crew. The crew men were identified as reporter Julian Manyon, 31, sound man Trevor Hunter, 38, and cameraman Edward Adcock, 41, all of London. It was not known early this evening precisely how or when they had been found.

Both Jones and Fenton attributed the abductions in interviews today to military-linked security forces. "I think it was an attempt to intimidate us all, to indicate to us that the rules of the game here are a lot different than the rules we are used to," said Jones.

Correspondents for several American newspapers, including The New York Times and the Los Angeles Times, have said they have been harassed by unidentified men, family members have been followed and their houses have been watched by men parked in the Argentine-made Ford Falcons used by security forces here.

Since the beginning of the South Atlantic crisis almost six weeks ago Argentine authorities have arrested three British journalists, who are being held in the southern city of Ushuaia on charges of espionage. The three, Simon Winchester of The Sunday Times of London and Ian Mather and Anthony Prime of The Observer, have been denied bail and face possible jail terms of two to eight years.

The recent abductions particularly disturbed Foreign Ministry officials here, who noted they were likely to be connected with the military government's campaign of violence against internal opponents from 1976 to 1979. Following the military takeover in 1976, thousands of people disappeared in Argentina, often after they were seized on the street by plainclothesmen riding in Ford Falcons.