This has been a particularly lovely fall, decorated with sunshiny days, blue skies, warm temperatures and almost no rain. The weather has been perfect -- for collecting leaves.

Just ask Vernon Ham.

He has raked leaves 30 autumns now for the D.C. Department of Sanitation. And out of all of them, he says, the conditions this fall have been the best for him to do his job.

"We can really have problems if the wind gets bad or if it rains or if it turns cold and freezes the leaves together," Ham said recently, as he paused from raking leaves into the hose of a giant vacuum cleaner.

None of those things has happened this fall.

Most of the leaves fell within a two-day period. There have been no wild winds to scatter them. There has been hardly any rain to turn them into partially rotted mush. And there have been no freezes to create the curb-side glaciers that have to be chiseled apart.

It has all added up to smooth leaf collections in most Washington area communities. By the end of the season -- late December or early January -- a total of 574 workers using 165 vacuum-equipped shredder trucks and trailers will have collected more than 267,000 cubic yards of leaves -- enough to fill more than 168 Metrobuses, without the passengers.

This year, D.C. is manning about 16 of the special vacuums a day in its effort to clean up and shred more than 10,000 tons of leaves by the end of January. A force of about 250 men is currently assigned, including 75 temporary workers, according to Joseph O'Donnell, chief of street cleaning.

Collections in Fairfax County, where the streets in front of 17,000 homes must be vacuumed, are just about complete.

"We will complete the third of three passes through the county by next Tuesday," said Veril Tielkmeier, director of the division of solid waste. "Everything has been perfect for getting the leaves. The weather was dry. The leaves came down all at once. We got most of them our second time around. Now we're just getting the scraps."

Last year, collection crews in the county raked in 60,000 cubic yards of leaves. The 30 temporary workers and 12 regular employes this year are expected to top last year's totals, Tielkmeier said.

Montgomery County workers have a challenge. With a crew of 150 men, 50 trucks and 40 leaf vacuums, the county gave itself two months to negotiate 750 miles of roads and collect leaves from a 66-mile-square suburban tax district, where residents are assessed a special tax to have their leaves collected. A similar tax is charged in 12 "sanitary districts" in Fairfax County. In most other jurisdictions, leaf collection is included in regular county and city taxes, or considered part of the trash pickup.

"Already we're 500 truckloads ahead of schedule," said Patrick Tracy, who is in charge of Montgomery County's leaf collections. "And we still have until Jan. 1 to finish the job."

Five Alexandria crews of two men each will complete their collections on Christmas Eve. One citizen made their job a little easier this year by requesting that 250 cubic yards of the leaves collected in his neighborhood -- enough to fill five regular Metrobuses or 2 1/2 of the "stretch" variety -- be dumped on his three-acre garden spot.

About 90 men in Prince George's County are nearly finished with their coverage of that 600-square-mile jurisdiction. The 16 crews also use vacuums that shred the leaves and blow them into trucks. Last year 2,100 truckloads of shredded and bagged leaves were collected in the county, with the amount expected to climb this year, according to a spokesman.

A brigade of 16 concrete and asphalt trucks trailed by vacuuming machines operated by 32 temporary employes has swept through Arlington County twice already, with a third pass to be completed by Christmas, according to William Bullard, the county maintenance supervisor.

Already, Arlington's collectors have picked up more than the 55,000 cubic yards recorded last year, because they were able to get most leaves on their first pass through the county.

If leaves could still be burned, disposing of the area's annual crop would be a simple matter of striking a match. But air pollution laws and regulations throughout the area generally prohibit the open burning of leaves. So jurisdictions have to find ways to get rid of their mountainous collections. There are generally three approaches, after a temporary stockpiling:

Taking the leaves to a landfill; paying to have them hauled to private farmland to be used as mulch and for landscaping; or allowing local residents to scoop trash bags full to dump on their backyard gardens and their lawns to help grow the grass -- and the leaves -- of 1982.