It was another languid August afternoon, and the temperature was rising in the air-conditioned White House press room.

Before deputy White House press secretary Larry Speakes finished his midday briefing last Tuesday, a presidential statement on controversial tax legislation was called "dribble," one reporter wanted to know about President Reagan's stand on bestiality and necrophilia, and the exasperated Speakes declared:

"This is a foolish briefing . . . . I tell you what: I challenge any news organization here to reprint this briefing in full in their newspaper."

So it goes in the dog days of summer at the daily White House briefing, alternately one of the most serious and one of the most bizarre rituals of Washington.

The briefing Tuesday began with Speakes' reading presidential quotations from a congressional meeting during which Reagan pushed for the tax increase bill, saying it would lower interest rates.

A reporter interrupted: "If you really want us to take this dribble down, you've got to go slower."

Speakes continued to describe the benefits of the bill, saying, "Real estate, auto, construction and related industries will be very happy," but he was interrupted by Sarah McClendon, the persistent correspondent known for throwing barbed questions at presidents, most recently at Reagan.

Speakes: "Choke it down Sarah, I've got a little bit more."

Another reporter: "She keeps bubbling up back there."

McClendon eventually asked about the list of promises Reagan made about economic recovery: "Can the president document this? Can you provide us with any proof this would happen?"

Speakes: "Sarah, I am not a prophet, nor is he."

When McClendon persisted, Speakes offered to explain supply-side economics, but that did not satisfy her. "Would you please give us the documentary proof that he has?" McClendon demanded.

"Look, Sarah. Look, look, look. I'm not the president. You can't sit here and badger me like you did him, now," Speakes replied.

Another reporter: "Larry, she has the right . . . ."

Speakes: "She has a right to the question, and I have a right to refuse to answer the question. I didn't."

Then ABC television correspondent Sam Donaldson asked about the tax increase.

"Deficit reduction, Sam," Speakes intoned.

When Donaldson protested, Speakes retorted: "This is not a debate society, Sam. If you want the facts, I'll be glad to give them to you. If you want to debate, I'll bring on a debater."

"This is a foolish briefing," Speakes sighed. "Had enough? I have."

It wasn't over yet.

Lester Kinsolving of Globe Syndicate, pointing to a published report that the government hires people regardless of their sexual preference, wanted to know, "Does President Reagan believe that the United States should be represented by all the many kinds of announced sexual preference or not?"

Speakes: "I haven't heard him advocate a quota system of sexual preferences for government employes."

Kinsolving: "I understand that. Does he believe that you should hire all kinds of sexual preferences. I mean, there is a wide variety."

Another reporter: "How many kinds are there, Lester?"

Kinsolving: "Well, there is necrophilia, bestiality, sodomy . . . . I just want to know, where does the president stand on this?"

Speakes: "Is there a serious question anywhere here?"

In fact, Speakes has come to expect such tangents, if not particularly to enjoy them. He thinks the White House briefings should be more orderly, like the State Department's briefing, but he's resigned to the fact they never will be.

The midday White House brefings are "so much of a ritual stage play," he said.

"Everyone wants to be a comedian," he lamented, and he often responds in kind. "Humor," he said, "is your greatest weapon" when confronted with questions like Kinsolving's.

One result of the sessions like the one last Tuesday is that Speakes now conducts an early-morning briefing in his office that is usually less combative, and, in the view of some reporters who attend, more useful.

And sometimes, when the irritations are too much for the unflappable Speakes, he delivers a lecture, as he did July 22.

"On August the first this year it marks my 14th anniversary in Washington, D.C.," he said.

"When I came here I called up the phone company and I had a phone installed and had my name put in the phone book. And since that time it has remained in the phone book . . . . I have always felt strongly about that, if I'm in the business of being a spokesman and receive a high government salary, then I should be available to the press.

"However, prior to this week -- and I don't mean to call any names and at least one of them's here, if not two -- I have been awakened twice at 5 a.m. . . . This morning I was awakened at 5 a.m. on the subject of the French imposing the -- saying they were going to violate the sanctions on the Soviet natural gas pipeline . In neither case did I have an answer.

"I give out my number thinking that you should probably reserve it for -- "

Reporter: "World War III?"

Speakes: "Russians crossing the border in at least division strength . . . ."