It should have been a holiday.

Yesterday was the warmest day here since last September and it put the Capital in a sensuous and sentimental mood.

The National Weather Service had the satistics - 85 degrees, a record high for 1977. But in the streets and parks and shops, there apparently was a feeling that the bitter, history-making winter finally and officially was over.

People stooped to caress plants and flowers in downtown parks. Smiles came easily. Only a few wisps of clouds broke the monotony of a crystal-clear sky.

"It's erotic, that's the word for it," said artist Robert Williams, sitting in a Georgetown gallery and longing for the white sands of a Florida beach.

Williams extended his lunch hour to watch women on the streets, who became "a little more sexy and exciting. It's fun when the girls are dressed as skimpy as possible," he said.

In Farragut Square park, a young man with a long telephoto lens focused his camera on unsuspecting women relaxing in the grass nearby. The park was jammed at lunch time with shirt-sleeved workers who mobbed carry-outs and sidewalk vendors in their brief escape from the confines of their offices.

It was a day for fantasizing, and the usual flow of paperwork that characterizes Washington slowed to make way for day dreams.

Clerks, secretaries and telephone operators all said their concentration was muddled by visions of strawberries, tennis rackets, lemonade and childhood memories.

Along Independence Avenue, golden, red and white tulips stood like contestants in a beauty contest.

A young couple in blue jeans and track shoes kissed through two walk lights on the corner of 17th and M Streets downtown.

"Everybody should have a day off," said Irving Goodman, a technical librarian at Group Health, Incorporated. The weather took him back, Goodman said, to Easter Monday holidays from school and egg hunts at the Bearskin Missionary Church in his native Clinton, N.C.

Everyone, it seemed, wished to be elsewhere engaging in pleasureable activities that only a few yielded to.

Araminta Coleman, a GHI secretary saw herself in Maine, "eating lobster on the seashore," but she settled for a 45-minute lunch break with a novel.

On the steps of the Freer Gallery, Smithsonian special policeman, Leo Howard said he longed to get out of his uniform and "find a cool spot in that park under one of those trees."

In terms he might have applied to an admired woman, Howard called the day "beautiful, gorgeous, very tempting."

Across the Mall, Dave Wills was having a slow day at his hot popcorn stand and gazing enviously at a nearby merry-go-round loaded with squealing children. A jazz band tugged his attention in the opposite direction.

Taxi driver Paul Washington wanted to spend the day at the zoo, or ride the Metro for the first time, instead of hustling fares, as he did.

Clerk Joyce Ward said she "should be in Hollywood, instead of at a desk," as she hurried into her Southwest office building.

Workers who answered the ccall of duty said they felt they should capitalize on the stimulation of yesterday's nearly perfect weather before the laziness of Washington's long, humid summer sets in.

"It's like a summer day, only the heat's not so bad," deliveryman Odell Mitchell observed as he held up the brick wall of the lithographic company where he works.

Mitchell said he heard weather forecasts for 90-degree heat today but "I sure hope it's wrong," he said.

Weather service forecasters said, however, that the temperatures will be "unseasonably warm," for the rest of this week. Instead of the normal sweater and light-coat weather of 46 to 67 degrees for this time of year, the area will have highs of 85 to 90 degrees during the day, and low temperatures of 55 to 60.

So it appears that the happy medium of yesterday was appropriate for city residents who followed their whims, as inventory control officer Gene Phillips did.

Phillips, a native of Washington, said he blistered his feet in a full day of walking among the museums and attractions on the Mall, seeing many of them for the first time in 15 years.

At Farragut Square, a fantasy that might have been anyone's was fulfilled for a retiring Mayflower Hotel employee. Friends salutd him with an outdoor banquet, served on fancy linen with candelabra, by formally attired waiters, while an acordionist entertained.

In Georgetown, a business-suited man was one of numerous grown-ups who unself-consiciously strolled along licking ice crean cones.

"It's just a glorious day," he noted.