Presidential contender Walter F. Mondale visited Capitol Hill yesterday on an apparently successful mission to convince concerned fellow Democrats in the House and Senate that the "Fighting Fritz" of the primaries still exists.

At the same time, Robert S. Strauss, party veteran and chairman of President Jimmy Carter's reelection campaign, told reporters that Mondale has asked him to assemble a Kitchen Cabinet of seasoned Washington political advisers to help the campaign find its footing.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who the day before had grumbled that Mondale has "allowed himself to be punched around by Reagan," said yesterday that Mondale "did sensational" in his meeting with about 200 House Democrats, satisfying the crowd that he will run an aggressive, hard-hitting, "shirtsleeves" campaign.

"Tip, I think I'm out there slugging," Mondale told him, according to O'Neill. The Speaker added, "The question is, is the press showing it?"

While acknowledging the importance of the candidate's television and media appeal, O'Neill lamented, "If only he could talk to people head on head, he's so talented . . . so brilliant, the election would be a landslide."

Mondale drew equally positive reviews after his meeting with 35 of the 45 Senate Democrats. The senators described their end of the exchange as suggestions, rather than criticism.

Sen. Edward M. Kennedy (D-Mass.) called the meeting "excellent, upbeat," and said he had made the point that "we ought to be on President Reagan's back, not Fritz Mondale's back."

Kennedy, plunging into a pack of reporters in contrast to his usual hallway behavior, said, "There was a strong feeling of 'Let's get on with the campaign' . . . . I think there was a bonding factor that came out of the meeting . . . . I think it was the strongest indication of support for a presidential candidate since I've been here."

Democrats on both sides of the Capitol vowed to improve coordination with the Mondale campaign in their home states.

Strauss, meeting with reporters at breakfast, described the Mondale operation's request that he set up an advisory group as "a heavy and dramatic change in that campaign."

He said Mondale campaign chairman James A. Johnson approached him with the request on Tuesday, the two met for two hours Wednesday and Strauss spoke with Mondale by phone early yesterday.

Johnson, asked if the Strauss group is an acknowledgment that, as critics have charged, the staff has been too isolated, said, "It is an acknowledgment that it is critical that everybody have avenues for participation that will work."

He bristled, however, at the suggestion that Mondale has been shut off from the advice of key Democrats. "That's one thing that's been so unfair," he said. "I don't think there's ever been a candidate more in touch with the leadership of the Democratic Party."

Among those Strauss said he plans to call on are prominent Democrats with a mix of campaign, White House and Cabinet experience, such as Washington super-lawyer Clark Clifford; political strategist Robert Keefe (a key adviser to Mondale's primary opponent, Sen. John Glenn of Ohio); Johnson administration official Harry C. McPherson Jr., Carter administration official Anne Wexler, black leader Vernon E. Jordan Jr., AFL-CIO president Lane Kirkland, former defense secretary Harold Brown, and Democratic activist and fund-raiser Pamela Harriman.