Urged by love of homeland and balmy breezes on a perfect spring day, some Washingtonians celebrated their ethnic roots by marching and munching yesterday while others proclaimed the latest political cause.

Approximately 5,000 people, many representing area synagogues and Jewish youth groups, walked a scenic 10-mile circuit through downtown Washington to raise the spirit of solidarity with Israel and an estimated $125,000 for the cause.

And while many of those marchers came downtown, several hundred area Thais gathered in Silver Spring, making good use of the warmth and sunshine to belatedly fete the Thai new year (April 13) on the occasion of the 200th birthday of the Thai capital, Bangkok.

But while those events went ahead as planned, a Falls Church salesman found that despite the day's obvious attractions and plenty of loving care, he could not get much support to sprout for the British position in the Falkland Islands dispute.

Jim Holeman billed himself as chairman of Friends of the Falklands, passed out leaflets and blared his message through a loudspeaker on crowded Lafayette Square, but almost nobody came to his rally.

"Ladies and gentlemen, we need your support and so do the British. Let's show them we support them . . . and oppose the subjugation of 1,800 people in their homeland," Holeman urged as he tried to rally support for the inhabitants of the small British-controlled islands invaded by Argentina this month.

But he was competing with the Ground Zero antinuclear rally across the square and the gusts of wind that kept knocking down his little "I Back Britain" signs planted in the grass like spindly saplings. The antinuclear folks and the winds ultimately won.

What little attention Holeman drew came from curious tourists attracted by a nearby television camera crew. Another man, a tourist from Carey, Ohio, stopped by just to argue.

It's a bloody little island," the man told him. "Why not let the British go back to Britain and let the Argentineans have it?"

But Holeman was undaunted. "This is a grass-roots American effort," he proclaimed. "We're not going to let it drop."

The "Walk Celebration 82," organized by the United Jewish Appeal Federation of Greater Washington, led by Capital Centre owner Abe Pollin and former Washington Bullets star Wes Unseld, was a much greater success.

Behind them stretched a procession more than two miles long that wound from the Washington Monument, up through Georgetown, back downtown past the White House and over to the Capitol before returning to the Monument.

Most carried cards pledging from 50 cents to several dollars for the charity for every mile walked. Most of the walkers, dominated by some 40 busloads of youngsters, had little trouble making the full 10-mile trek.

Pollin, despite a double bypass heart operation last year, set the pace, side by side with Unseld, the massive former center who is now a vice president of the Capital Centre.

"He walks fast, I was jogging and I could hardly keep up with him," said 12-year-old Chad Karp of Unseld's giant stride. "I don't think I would have made it if it wasn't for him."

UJA spokesman Marc Breslaw credited concern over recent turmoil on the West Bank and anxiety over the planned Israeli turnover of the Sinai desert to Egypt next week for increasing the turnout of pledged walkers from 3,000 last year to 5,000.

"I think they should have all the land they can get," said Sharon Silverman, a bubbly 14-year-old walk-a-thon veteran from Potomac who looked forward to the end of the march, when she would be able to "munch out" on food from tents near the Monument. "Has any other country given all their land back after they won a war?"

Miles away, it was the Thai festival on the grounds of a Silver Spring Buddhist temple that slowed traffic on Georgia Avenue yesterday.

The Songkran Festival, or Thai New Year, as put on by the Wat Thai Monastery, was a gentle mixture of spicy food, bright Thai costumes, religious ceremony and folk dances performed on a small outdoor stage. Drawing Thais from as far as Camp Springs and Alexandria, it was largely a welcome get together for many recent immigrants.

"This is my second time," said Nirun Vongpukkeaw, 25. "Last year it wasn't as big as this year."

By 2:30 most of the pots of food sold from tables lining the yard were empty. "Everything was so very good, it was all sold out in an hour and a half," said Vongpukkeaw.

Onlookers crowded around the stage to watch an exhibition of Thai boxing, augmented with karate-like kicks, by two youths from the Thailand Military Academy clad only in brightly colored shorts. The spectators voiced comments in the Thai language with each blow landed and cheered when the intense but friendly match was called an amicable draw.

The fragrance of chicken curries, beef tripe and beansprout soup still lingered under the trees, but the obligatory beauty contest near the end of the festivities had a distinctly American flavor.

"Hey, that's my sister," yelled a young man in Thai as one of the five shy finalists in traditional costumes was introduced.

There were only five contestants. Wassana Courtney, 17, of Herndon, won the second-place trophy. Courtney said she figured her manner was too American for the judges.

"They want you to be shy and quiet. I'm not like that," said the high school senior, who wore a traditional silk dress from the homeland. "I like to dance and to go out and boogie, you know."