RONALD REAGAN'S fireside summit was ashes to serious arms controllers, who for political reasons may not get around to saying so right away. Conservatives were also reluctant to react. They did not wish to express immediately the relief they felt that nothing had happened in Geneva. They wanted to be sure that everyone understood how deeply they disapproved of their president for playing with fire by meeting with a Soviet leader.

The night the President returned, the hard core that long ago launched him on the road that led to Geneva, was gathered at the Hyatt-Regency for a roast of Jesse Helms, who has never failed them.

The humor was the of the robust variety that marks their festivities. Senate Republican leader Bob Dole called the guest of honor the "Rambo of the Geritol Set." Preacher Pat Robertston made jocose references to Teddy Kennedy's swimming lessons and Rep. Bob Dornan, the distinguished tie-grasper from California made scathing reference to the "moderate squishes in the White House" and Helms, when his turn came, defended Barry Goldwater from unspoken charges of veering from the true gospel.

It was the one place in Washington where Donald Regan, who provided the only genuine news from the mountain-top with his remarks about women's inability to fathom world issues, might have felt at home.

The mood in the hotel ballroom was that of parents whose teen-age son has stayed out late with the car and finally turned up. They have to be severe until he realizes just how much he has put them through.

Ever since the president announced that he would meet with Gorbachev, the right-wing has been in the grip of morbid fears of a sell-out. Awful suspicions that Nancy Reagan is a closet peacenik have gnawed at them. No word from the president could persuade them that Star Wars -- their new Holy Grail that would eliminate all need for any future meetings with any Soviet -- would somehow come crashing down.

By the time they gathered, they knew that nothing of consequence had transpired by the fire. Huge Howard Phillips, a true believer, talked darkly about the harm the president had done by sitting down with Gorbachev and "creating an environment that could make the arms buildup more difficult."

When asked what they had wanted from the summit, a young man who identified himself as a leader in the conservative movement at Georgetown University said simply, "I wanted him not to go."

So when the Helms and his entourage had hurried off to greet the president in the House chamber, they moved to the television monitors to hear his report to Congress in a critical frame of mind.

When Reagan announced that, as a consequence of the lamentable encounter, Gorbachev will be coming to the U.S. next year, there were groans of "Oh, no."

When he said that they "did make some measure of progress" in reducing nuclear tension, there was a thunder of applause on the television. Dead silence was heard in the Hyatt-Regency Ballroom.

The talk of replacing all offensive weapons with a defensive system of having Soviet students swarming all over the U.S. while innocent Americans went to Russia drew heavy sighs.

The true believers applauded only once. That was when the president promised that we would continue to support the Freedom Fighters. There were appreciative murmurs of "hear, hear."

At one point the camera panned to George Shultz, who was sitting in the front row of the chamber. "There's the real villain, whispered Richard Viguerie, the Tory mail-order king. "Conservatives feel he is soft on communism. He thinks understanding each other is the key to peace."

The right-wing has never wanted to believe the worst of Ronald Reagan. It has always sought a Rasputin. While he was White House Chief of Staff, James Baker filled the bill. As Secretary of the Treasury, he has become less sinister. Shultz has replaced him as the source of infection.

Shultz' resistance to supporting anti- Communist rebels in Angola makes right wing blood boil. The toastmaster of the dinner, William Gribbin, received huzzas when he announced that Helms would give out door prizes before he left, copies of "George Shultz' Summit Cookbook, 40 Ways to Eat Crow."

When the president wound up with a Thanksgiving Day flourish, did the vigilantes give way to applause.

"How do you spell relief?" said Viguerie. "He didn't drop the other shoe."

Reagan had given them reassurance they needed: There is no danger of arms control any time soon; that there had been no wild fireside talk about a test-ban treaty or any such obscenity.

Ronald Reagan had only seemed to stray from the path of rightness. He has come home. All will, in due course, be forgiven.