Washington arrived at their offices yesterday fully expecting the worst as 78-degree thermostat settings went into effect, and most weren't disappointed. But, always protective of their image, many refused to give up the symbols of professional dress.

A skirmish over fashion broke out on Capitol Hill;

In restaurants, ties were loosened and jackets removed, but kept handy;

In retail stores, women wore sundresses but tried on winter clothes;

Office workers brought extra shirts to change into throughout the day, while others tried "thinking cool."

Many women, despite far more dress alternatives than men, stuck to long skirts, though some adopted options with the "dress-for-success" look.

"I've been busy looking for things to wear without a jacket," said Rep. Geraldine Ferraro (D.N.Y.), who was wearing a V-neck cotton jersey dress. "My suits are just too hot for now." Ferraro thinks men should feel just as free to go without jackets as women do. "I'd like to see that all men are treated in Congress as women members."

Ferraro had gotten a "Dear Colleague" letter from Rep. Morris K. Udall (D-Ariz..), self-appointed chairman of his own "Congressional Comfort Caucus," with a push to "liberate men from the summer tyranny of coats and ties. We can simultaneously strike a blow for energy conservation."

In recommending summer shirts as appropriate attire, Udall urged his colleagues to "Arise! You have nothing to lose but your discomfort."

Sitting in his 78-degree office with his tie and collar loosened, Udall said, "Every time the (roll call) bell rings, you see a parade of congressmen carrying their coats over their arms to put on the second before they enter the chambers. It doesn't make sense."

By midday yesterday, Udall had 30 colleagues signed up to support his no jacket "Comfort Caucus."

But, meanwhile, Rep. G.V. "Sonny" Montgomery (D-Miss.) had kicked off a counter movement to "maintain the dignity and decorum of our House proceedings." He suggested men's coats remain on, but offered an alternative.

"The best way to offset the temperature problem," he said, "would be to cut off the television cameras until after the August recess . . . [This would] not only make the temperature more comfortable but it would save time in the legislative process."

At the White House, Jo Carpenter, a press aide, was "making do" with a woven raffia fan brought from home and a cotton sundress that she had made more demure by pairing with a cotton vest. "You don't want to be too bare around here," she said.

Marc henderson, associate White House press secretary, took less drastic measures. He kept his suit vest on, but eventually rolled up his long sleeves.

In the Commerce Department basement offices, one secretary was having problems making concessions to the heat. "I wear a girdle, and I wish I could take it off," she said. "And I'm too old to go without stockings. I try to make a lady-like, professional appearance, so I can't wear sundresses."

A fan in the doorway of computer specialist John Adams's office at Commerce helped circulate air. Adams was without a tie for the first time yesterday and admitted he felt less professional without one. "Everyone on the commuter bus from Reston wears or carries ties. But today, with the 78-degree rule, I felt I could give mine up."

Data base administrator James (Jim) Brown, who works in the same office as Adams, disagrees. Even last Friday, when the temperature hit 84 degrees in that office and before they commandeered a fan from another office, Brown was wearing a tie with a loose knot, and a short-sleeve shirt.

"Temperature is no excuse not to look professional," he said. "If you have to meet with upper management, you have an image to portray." Later he add, "They pay me enough to look professional."

At Sans Souci, where the heavy wood front door was anchored open to help circulate fresh air in the 85-degree restaurant, former Navy secretary J. William Middendorf, lawyer Arthur Becker and banker Nadeem Maasry were jacketless and using their linen napkins to mop their brows.

Keeping the thermostat up is not a requirement for museums. Just the same, Renwick Museum director Lloyd Herman has his private progarm for energy conservation. He keeps his office dark and two jackets on a valet stand in his office ready to wear if visited by another curator or called to another museum.

In spite of yesterday's heat, city planner Margot Wagner used her lunch hour to try on winter coats at Raleigh's. It was not a matter of energy but economy. Wearing a three-year-old sundress, she figured that the hot weather promotional sales not only saved her a lot of money, but gave her a better selection for her hard-to-fit 5-feet-11 height:

But it wasn't the clothes you wear as much as "thinking cool" that district building administrative aide Thelma Blackwell thinks makes a difference. She pictures herself on Icelandic Airlines coming from Iceland, and her whole body feels cooler, she insists.

Postal clerk Eunice Thomas can measure the heat of the day by how many shirts she wilts and has to change in the Calvert Station branch. She counted on yesterday being at least a two-shirt day.

Downtown at the National Electrical Manufacturers Association, vice president Bob Smith instructed his laundry yesterday morning to stop starching his shirs because "a softer shirt is much more comfortable in the heat."

Public relations manager Dan Shipp says he and others may have to take up the "rumpled" look of the Haspel suit, whether it was "in" of not.

At Georgetown University, Father William George, S.J., who works in the university president's office, says he has to look fairly formal, but he was caught with his clerical collar undone. "Unbuttoning my clerical collar is the same as loosening a tie," he said.

But wait.

"We heard cries of anguish when we went to 68 degrees last winter," he said.

The worst may be yet to come. CAPTION: Picture, Nadeem Maasry, Arthur Becker and J. William Middendorf, by Gerald Martineau