The winner of last night's presidential debate depended entirely on where you happened to be watching it.

"My reaction is that I think Mr. Mondale's performance was just about like the Cubs' today," said Secretary of Agriculture John Block at a Capitol Hill Club party thrown by the Republican National Committee and Reagan-Bush '84. "The president came through."

"I'd say Mondale won," said Ed Black, an international trade attorney and host of one of 500 parties held in District Democratic homes to raise funds for local registration drives. "Reagan's is an ostrich presidency. He's hiding from the future."

The president could do no wrong with the 400 or so Reaganites at the Capitol Hill Club party, where Block and Lyn Nofziger, consultant to the Reagan campaign, watched the show. "I think that Mr. Mondale came across better than he ever has," said Nofziger, "but he clearly did not win this debate, and he had to win. He goes out of here a loser."

The crowd was mostly young, clean-cut and preppy. Many wore red or gray or navy. One man wore a "Fritzbusters" button. He said he got it at the Heritage Foundation for $2.

The guests stood around sipping drinks from one of the half-dozen open bars, eating potato chips, pretzels, veggies and cheese. Nofziger said he thought people were "excited."

Bill Greener, director of communications for the Republican National Committee, talked to Nofziger about why there were so many young people in the crowd. "Why are all the young people for Reagan? All we have to compare is Ronald Reagan and Jimmy Carter," said Greener. "I'll take my chances on Reagan any day of the week."

Downstairs were two small TVs and a big-screen set. On the second floor were four TVs. The audience sat on couches and on the floor downstairs, and around tables upstairs. They laughed at Mondale. They booed and hissed any comments he made alluding to Reagan's policies or platform. Snoring noises were heard during Mondale's longer remarks. During one long answer, a young woman turned to a friend and said, "Marty, he's really boring me."

When Fred Barnes of the Baltimore Sun asked Reagan why he did not attend church services regularly, the crowd moaned. Someone yelled out, "C'mon, that's old." And when Reagan replied, ". . . the Lord understands" the crowd cheered.

On the third floor was a TV for VIPs. That's where Nofziger kicked off his shoes, sat back on a pale blue couch and passed munchies to Block, who sat next to him. Margaret Hance, co-chairwoman of Reagan-Bush '84, was also there.

At one point Mondale compared declining farm income to a grain embargo. Everyone in the VIP room grinned and looked at Block. The secretary of Agriculture shook his head, laughed and said about Mondale, "He felt so damn threatened, he had to say something."

After the debate Block commented further. "I thought the president was great. I personally was pleased. He came out and pinned the tail on the right donkey. The grain embargo was the result of the Carter-Mondale team.

"I was proud of him."

Blcok wasn't the only one who thought so.

"I think Ronnie was absolutely at his best. He made goosepimples," said Harriette Sachs, a volunteer for Reagan-Bush '84. "The things he said were so . . . um . . . full of charisma. I've worked for him, not paid, for 11 months, and I'd work another 11 just to see him reelected."

A cab ride away, at Ed Black's Logan Circle town house, it would have been easy to assume the place was full of Padres fans celebrating their team's victory. But the pennant had been decided hours before -- now it was Reagan versus Mondale.

When the crowd of 50 young attorneys, lobbyists and Hill staffers weren't intently watching the proceedings, they were reacting to them. Cries of "Go for it!" and "He's smokin' now!" greeted Mondale's words. Reagan's fumbles evoked satisfied grins.

"Mondale's doing well," said D.C. Councilwoman Betty Ann Kane at mid-debate. "He's breaking out of that staid mold. Reagan seems very hesitant."

And once the dust had settled: "Vice President Mondale did extraordinarily well and the president did very badly," said Sen. Paul Sarbanes' (D-Md.) administrative aide, Marvin (Bud) Moss. "I would certainly hope Mondale's performance can close the gap in the polls -- the future of this nation depends on it."

"Of course, my opinion tends to be weighted in one direction," said Mary Helen Thompson, Sen. Paul Tsongas' (D-Mass.) press secretary, "but I think Mondale had a message. The president got bogged down in facts and figures with no message."

Concurred Miriam Chalefsky, a consultant on education concerning the Holocaust: "Mondale spoke like a man, not a wimp. I didn't understand the president's statements about the economy. He and I have read different economics books."

Black's party was part of a fundraising effort dubbed "America for Mondale-Ferraro." The idea was to raise at least $500 at each of the thousands of parties held in Democratic homes across the nation, with the funds earmarked for local voter registration drives. The Washington parties ranged from an intimate dinner for two couples at the William McCormick Blairs, to a huge bash at Numbers disco, to serious debate-watching gatherings such as that at the home of Ann Howard, Hubert Humphrey's niece.

Most of the parties weren't originally planned around the debate but around a 30-minute paid Democratic political message that was to have aired on ABC before the debate was scheduled for last night. But the parties went on anyway, even though a number of prominent Democrats preferred to watch their man in the privacy of their own homes. Still, there was no shortage of advice for the candidates or predictions on the debate's outcome.

"It's like a football game," said Sen. Lawton Chiles (D-Fla.) at a party at the home of former social secretary to Rosalyn Carter Gretchen Poston. "Mondale can't get the ball back with one big play. But the American people love a horse race. I would advise him not to knock Reagan out. It's Mondale's chance to look and act presidential."

"Mondale has to forget the facts and figures and present his vision of the next four years," said David Rubenstein, Carter's deputy domestic policy adviser and author of the infamous 1980 debate briefing book. Rubenstein, who has sent memos to Mondale's advisers, feels confident that there won't be another "Debategate" episode: "They're being very careful with security this time."

"I would call it a 'joint appearance' . . . it's no debate," said Sen. James Sasser (D-Ky.). "If I were Mondale, I would talk about values and contrast mine to those of the president. Reagan might suffer by comparison. One thing's for sure, it can't get any worse for Mondale. When you're 20 points down, that's the bottom.

"If Reagan has to answer questions for 1 1/2 hours, he's bound to state facts incorrectly," said Sasser.

"There's always a chance," said Abe Pollin, Capital Centre chairman and owner of the Bullets and Caps, of Mondale's election prospects. "As the Bullets' coach said in 1978, 'The opera isn't over till the fat lady sings.' "

"They say Mr. Mondale has never lost a debate," said his wife, Irene.

"Mr. Reagan has never lost an election," answered Pollin.