Every year about this time, as regularly as the arrival of frost in the parks and Salvation Army kettles on sidewalks, a new season descends on the national capital accompanied by much handwringing, bureaucratic breast-beating and feigned anguish.

It is the season of the budget leak.

You can't find the leak season on any calendar or even in the "Old Farmer's Almanac." Ordinary folks hardly notice it, for good reason. It is a time of year reserved for Washington insiders, people whose livelihoods depend on numbers in the federal budget.

The celebrants are normally confined to a handful of bureaucrats, journalists and lobbyists, who have discovered the ultimate truth about government: politics isn't about charisma or flashy speeches; it's about how the pie is divided.

The leak season is best observed in the pages of newspapers. One can find leaks meant as trial balloons, leaks meant to advance administration policy, leaks meant to sabotage it, leaks meant to return a favor from a friendly reporter, leaks from White House aides, members of Congress, bureaucrats and lobbyists.

The leak season has been around for decades, but has become far livelier during the Reagan years.

"I do think it's getting worse all the time," said Edwin L. Dale Jr., public affairs director for the Office of Management and Budget. "Twenty years ago there was hardly any of it; 10 years there was some. It's the last five years that it has really gotten out of hand."

This year the season officially began Dec. 11, shortly after OMB Director James C. Miller III gave President Reagan an OMB list of spending cuts for fiscal 1987. It is expected to continue, through various incarnations, until a final budget document is sent to Congress in February.

"The first stuff had to come from the White House," Dale said. "I don't know their motives. I've been trying to figure them out for five years."

The Wall Street Journal was the first leak recipient. It heralded the advent of the season Dec. 12 with one report, then followed a day later with a more detailed account of dozens of proposed cuts that Reagan had told Cabinet officers about during a White House meeting. The reports were attributed to "administration sources."

On Saturday, The New York Times, quoting a document supplied by a White House source, said the OMB had recommended that the Federal Housing Administration (FHA) "be sold in its entirety" to "private bidders" in "the private sector."

The Washington Post reported that the OMB had recommended halting all federal spending for Metro subway construction and making new cuts in Medicare and Medicaid, attributing the stories to "officials" and "congressional and other sources." The Medicare-Medicaid story didn't surprise those at the OMB. "We all feel HHS the Department of Health and Human Services is a place that tends to be fairly leaky," Dale said.

If there is any doubt about what was going on it came Tuesday when the Mortgage Bankers Association called the first news conference of the leak season.

Association President Ronald F. Poe denounced the Reagan administration proposal to sell the FHA as "the latest and most outrageous in a long line of proposals that would, in effect, deny homeownership to moderate-income Americans."

Poe knew what was up. "We all know how things work in Washington," he said in a prepared statement. "A bad idea gets floated as a trial balloon and then everyone waits to see who takes potshots at it."

The potshots attract attention. Opposition builds. Those singled out for budget cuts rally together. Coalitions form, especially those representing monied interests. Lobbyists, and sometimes ordinary citizens that they attract to the cause, march on the halls of Congress and the administration. It's the Washington way.

The stakes are unusually high this year. The administration must propose enough savings to meet the $144 billion deficit target set for fiscal 1987 in the Gramm-Rudman-Hollings bill the president signed last week. To do so, about $50 billion in domestic spending cuts will be needed for the budgetary year that begins Oct. 1.

That's what the opening round of the leak season was about. Agencies can appeal the cuts proposed by the OMB last week. But if they do so the agencies have to come up with equivalent savings elsewhere in their budgets, Reagan told his Cabinet.

This means more leaks.

But the OMB doesn't seem worried. "There is nobody here contemplating suicide or jumping out the window," Dale said. "We don't like it, but there's not much we can do about it."