On the final Sunday of the decade the air was filled with softballs and frisbees and joggers tossed aside their sweatsuits as hundreds of Washingtonians streamed out into the sunshine and temperatures reached a surprisingly warm 61 degrees.

"People better enjoy it now," said a National Weather Service spokesman at Dulles International Airport. He predicted the temperature on New Year's Day will drop to a high in the low 40s as a large cold front descends from Canada.

Those planning to celebrate the arrival of the 1980s can expect New Year's Eve temperature to be in the high 30s, after a daytime high of 52, the weather service said. There will be increasing cloudiness tonight, and slight chance of rain.

Yesterday's unseasonably warm weather fell short of a record, 1971 high by seven degrees, said Bill Miller of the weather service's National Airport office -- still high enough to lure people like Frank Marut outdoors.

Marut, a retired 67-year-old Eastern Shore fisherman, was tying small canvas sails onto a 13-inch replica of a square-rigged, four-masted Flying Cloud clipper ship with his rope-burned hands while he sat on a park bench overlooking the Potomac River.

"It's a good day for sailing," he said, scratching the white stubble on his face, "or just sitting around remembering. A fine day."

Farther south along the George Washington Parkway, Claude Lawrence, 28, stared at a boat that looked less seaworthy than Marut's model.

"It's a 28-year-old Hartge Quadrant -14-feet long," said Lawrence of the vessel, dry-docked at the Washington Sailing Marina. He said he was glad it was a warm, sunny Sunday. "I've been working on this thing for eight months, trying to get her ready for next summer."

Off Fort Hunt Road in Fairfax County, 21-year-old Paula Raffaele twisted her shoulder length, brunet hair.

"I'm jogging [doing] a few jumping jacks, a little bit of everything," she said. "Four guys have tried to pick me up. What do they do to you people here?"

It was a day when 19-year-old John Lugmayer of Clinton decided it was time to forget about the work that normally fills his late December Sundays.

"I was going to work on my old Volkswagen until I woke up this morning," he said. "I brought out my 10-speed bike, oiled and cleaned it up and took off" along the Parkway bike trail. "I'll go about 40 miles today. I always enter the local races in the summer."

Racing was definitely on the minds of the Potomac River Laser Fleet, a group of recreational sailors who braved the 42-degree waters of the Potomac yesterday in their single-seat, 13-foot Laser boats.

Marshall Huffman, a 41-year-old tax auditor for the Internal Revenue Service, sauntered along the bike trail near Bell Haven Park with one arm on a walking stick and the other around his 40-year-old wife, Denise. He said he couldn't believe he was enjoying himself and not watching the National Football League playoffs on television.

"I told him we were going for a walk along the river like we used to do," said Denise. "I wasn't asking him."