"I understand President Reagan got up this morning and walked across the Potomac," said Bob Hope, who found the weather in Washington colder than his home in California.

"But it didn't count," Hope added after the laughs died down at last night's fund-raising gala for Wolf Trap Farm Park, at the Capital Centre. "They're going to make him do it again next summer."

But most people in the audience were thinking about last week, not next summer. The climax of the evening's first half was the introduction of members of the Redskins and their wives, who walked on stage, were kissed by Elizabeth Taylor and stood quietly while the crowd gave them a standing ovation, stomping, cheering and singing "Hail to the Redskins."

More people seemed to know the words of this anthem than "The Star-Spangled Banner," which was played by the Marine Band to open the evening, while the big video screens showed a flag waving, fireworks exploding, rockets taking off, fighter jets flying in formation and the U.S. hockey team beating the Soviets in the last Olympics.

Later Hope commented, "The Redskins have done an awful lot to unify the nation's capital. Washington hasn't seen such teamwork since the last time Congress voted itself a pay raise."

Hope, billed as the emcee for last night's gala to rebuild Wolf Trap's Filene Center, which burned down last year, was feeling ill and came on late, leaving the opening chores to singer and songwriter Paul Williams. The job was taken away from Williams after he introduced the opening acts, singer Stephanie Mills and dancer Donna Wood of the Alvin Ailey Dance Company.

"I thank Mr. Hope for letting me do this part of the show," Williams said as he left the stage. "I feel like a real grown-up now."

Hope--considerably more grown-up than Williams--devoted many of his jokes to the problems of old age.

"The president celebrated his 72nd birthday the other day," he said. "The way he's cutting things down, you'd think he'd lop off a few years." He also took the usual pot shots at his friends and colleagues. He predicted that next year "Dustin Hoffman may win both Academy Awards" for best actor and best actress. "But Academy Awards aren't everything," he said. "If you don't win an Academy Award you can always run for president."

Elizabeth Taylor appeared on stage briefly and engaged in obviously scripted dialogue with Hope about her recent visit to Israel, where she suffered an accident. "They were wonderful," she said. "They were so thorough. They went over every inch of my body. The first day, they put me on intravenous feeding."

"That must have been a lot of vitamins and minerals," said Hope.

"No," she answered. "It was chicken soup."

Hope's sharpest political joke of the evening was aimed at former secretary of state Alexander Haig. "Politics is like show business," he said. "One day, you're drinking the wine, and the next you're picking the grapes, as I was just saying to the doorman, Alexander Haig."

Haig knew that the end was near, Hope reported "when he walked into a meeting one day and found a black jelly bean at his place at the table."

Politics also was on Williams' mind at the beginning of the show. "I made a little resolution to spend more time in Washington," he said. "I'm not running for anything yet, but I like it here."

Looking out at the packed audience of 12,000--more than twice as many as Wolf Trap could hold--he made one of the evening's few economic jokes: "The only people who have better seats than the Republicans," he said, "are the Toyota dealers."

He also gave the evening one of its few solemn moments when he sang "We've Only Just Begun." After he wrote that song, he said, "an angel sang it for me. Her name was Karen Carpenter." He dedicated the song to Carpenter, who died Friday of congestive heart failure.

The most awkward moment of the program came during the performance by rock singer Meat Loaf, who drained a large bottle on stage in a couple of gulps, and dedicated one of his songs to those in the audience "who forgot to bring your gold cards tonight."

"All you who ain't never been to a rock 'n' roll show," he shouted, "you better get out of your seats and start boogieing with us." Then he left the stage and walked ominously toward the thousand dollar seats in the first row, which were quickly evacuated.

"This is what happens when you don't have any linebackers," said Hope, trying to quiet the mammoth performer who had wandered back to the stage and spent several minutes shouting, "how the hell y'all doing," before they finally managed to usher him backstage.

"The ten dollar seats loved him," an observer from that area reported later. "Somebody's getting even for all the times kids have been forced to go to ballet and opera."

A striking contrast was provided by Sammy Davis Jr., who spoke briefly after concluding his act with "Mr. Bojangles."

"I thank everyone responsible for letting me be a part of this evening," he said. "My roots in this area go back to the Howard Theater in Washington, when I was a part of the opening act with my father."

Robert Gray, chairman of the Wolf Trap Foundation, introduced senators, members of Congress and other celebrities in the audience, including Sen. John Warner (R-Va.)

Gray announced that before the evening's fund-raiser, $3,164,878.16 had been contributed to rebuild Wolf Trap, in amounts ranging from 3 cents to a pledge of $1 million. He also showed a film in computer graphics of an architect's concept of "the new, fireproof Wolf Trap II," and climaxed the evening with the introduction of Catherine Filene Shouse, founder of Wolf Trap.

"If it weren't for Kay Shouse," commented Hope, "we'd all be home in bed tonight."

Shouse, asked how she had enjoyed the evening, had a diplomatic answer: "Thousands of people went home happy."