The 11th economic summit of industrialized nations opened here today amid tension, tight security, anti-Russian jokes and the walkout from a press briefing of a U.S. diplomat who is expected to become the next ambassador to West Germany.

The walkout was staged by Richard R. Burt, the 38-year-old assistant secretary of state for European affairs who is Reagan's prospective choice to replace U.S. Ambassador Arthur Burns. Reporters had angered him.

More than 12,000 police threw up a heavy security net around the government quarter where the seven heads of state will gather Friday for their first plenary session. Six patrol boats stopped all traffic on the Rhine when Reagan arrived by helicopter from a government guest house 25 miles away.

West German Chancellor Helmut Kohl apologized to Reagan for the tight security, saying that it was necessary because of bomb threats. A bomb was defused in Bonn's diplomatic quarter yesterday, and three bombs went off in nearby cities last week but caused no injury.

There was tension this morning between West German police and U.S. reporters, who were delayed from entering briefings after the Germans refused to honor the press credentials they had issued.

But there was even greater tension in the White House briefing room in the Tulpenfeld Hotel when Burt gave reporters an account of this morning's meeting between Kohl and Reagan under ground rules that required the diplomat to be identified as "a senior administration official."

Some reporters laughed skeptically during the briefing, objecting to summaries that they thought failed to reflect the actual words of the two leaders. One reporter asked for a more detailed explanation. Another made a wisecrack.

Burt, whose identification was provided later by a White House official, said "goodbye" and walked off the podium. It had been a difficult day for the diplomat, who started out by showing up late for Reagan's arrival ceremony.

White House spokesman Larry Speakes said later that Burt, a former New York Times reporter, was "not used to the abuse that one has to take standing at this podium."

The Associated Press reported that a West German official, speaking privately, took issue with Burt's assertion that "the chancellor said that we must never forget and we can never forgive." The official said Kohl actually repeated his oft-stated view that "we have no right to expect that the victims of the Nazis forgive or forget."

Kohl and Reagan were clearly in good spirits on this blustery day.

Kohl told the visiting president that if he ran for election here he would "win by a very wide margin."

Secretary of State George P. Shultz interjected, saying, "I'm sorry, chancellor, but Reagan is needed back in the United States."

West German spokesman Peter Boenisch said that the two delegations, led by Reagan and Kohl, swapped anti-Russian jokes when they made small talk this morning.

One of the jokes, of which Boenisch did not identify the author, was, "Did you hear about the robbery at the Kremlin?" The punch line is that the robber stole next year's election returns. A knowledgeable source identified it as Reagan's joke to Kohl, who was said to have laughed appreciatively.

When Kohl visited Washington, Reagan told him that the late Soviet president Leonid Brezhnev had said, "I thank God I am an atheist."

After Kohl returned home, former chancellor Helmut Schmidt claimed credit for the joke, saying he had told it to Reagan.

Other than complaining about the cold, Reagan seemed to be enjoying himself during the opening stages of a trip that has been marked by continual controversy over the president's plans to visit a German military cemetery Sunday.

Reagan spent the night at the 700-year-old Gymnich Castle, the official West German government guest house which is now reportedly owned by a godson of Adolf Hitler.

Asked if he had seen the reports, Reagan said with a smile, "All I know is that after one night I found out there are no ghosts."