On a almost really hot day in what could be Washington's chilliest summer ever, the area was astir with activity yesterday.

There was watermelon-eating at Alexandria's 230the birthday party and a Spanish-American outdoor fiesta at a Northeast Washington church, and throughout the city taxi drivers glared at gasoline lines and talked aloud about another strike.

In Alexandria, Bill Winnie joined a watermelon-eating contest in Chinquapin Park and won face down. Disregarding the sticky watermelon juice running down into his shirt, Winnie bobbed his head in and out of a quarter of a watermelon, finishin it in just over a minute.

"I'm worried about Pepco and Vepco," said Jean Perez, another celebrator at Alexandria's Bicentennial Center, where men dressed as Revolutionary soldiers fired muskets into the air.

"With all this nice weather instead of the ususal heat and humidity, they're not making millions on air-conditioners," Perez said of the utilities. I hope "they won't have to raise their rate again," she said with a laugh.

The National Weather Service said yesterday that a metropolitan-area record that has stood since 1871 will be broken if the temperature here fails to reach 90 degrees by Monday. That temperature is considered the benchmark for what is uncomfortably hot.

Not since 1871 has it taken the Washington summer until July 9 to heat up to 90 degrees. The temperature in Washington yesterday rose to only 83, with a low of 60 degrees at 5 a.m.

Sunny skies and warmer temperatures, rising to a high of 88 today and 89 Monday, according to the weather service, are expected to continue. A forecaster said yesterday that it is a good bet that Washington's summer of '79 will break into the record books as the coolest yet.

In Northeast Washington, hundreds of people participated in a Spanish-American fiesta at St. Luke Catholic Church, 4925 East Capitol St.

In the Spanish tradition, there was a pinata full of prizes and candy for children to pull down. There was lots of Spanish food, Spanish music and such extras as a boutique of clothes on sale for prices as low as 25 cents for a pair of pants.

"I'm from Puerto Rico," said Ana Strothers, chairwoman of the church festival," and I had the idea to have an outdoor festival. People from the islands islike to do things outdoors. They had never done that here."

Although Strothers knows only one other person in the church's neighborhood who is from a Spanish-speaking country, she said the black Americans who live there have taken to the festival.

"It's been a huge success," said Marjorie Baker, a member of the church committee. "People who have never been anywhere near the islands have come and enjoyed themselves."

Around gasoline stations and taxi-cab stands in the city yesterday the main topic of conversion was a plan to have a three-day strike beginning July 16.

"Yeah, I'm going to strike for more money and more gas," said Mary Roberts, as she waited for a passenger outside the Madison Hotel.

"Losing money for three days isn't going to hurt me. I'm not doing anything out here but driving around trying to find a gas line. And when I find one I give all the money I got from these cheap fares."

But Bob Loman, who drives an ABC cab, said he thinks the timing of the strike is bad because during the week of the 16th the American Bankers Association will have a convention here.

"Those people [who attended the convention] ride the cabs," Loman said. "That's going to be the richest week for cab drivers in this town for the next two months. After the everyone goes on vacation around here."

On June 25, taxi drivers struck for one day and said their strike was 85 percent effective. The cab drivers have been granted a 10 cent increase per ride but are seeking a 10.5 percent increase on all fares. The strike, which has been called by the National Taxicab Alliance, is not being backed by the Professional Cb Association, another cab drivers group. CAPTION: Picture 1, Men drill in Revoluntary war uniforms at the Alexandria Bicentennial Center in commemoration of that city's 230the birthday; Picture 2, In the same celebration, a clown named Susan takes part in a Hula-Hoop contest; Picture 3, Lelia Browne reaches for a pinata and Tenom Browne watches at a Spanish-American fiesta sponsored by St. Luke Catholic Church in Northeast Washington. Photos by Margaret Thomas - The Washington Post