They don't know what to call it yet, possibly "Capital Compost," "MetroEarth" or maybe "Washington's Best," but flowers and vegetables love it, it will be free, and will be availbale By this fall in almost unlimited quantities for farmers, nurseries, parks and homeowners.

By whatever catchy name it's called, it will be Washington's 600-ton-a-day sewage sludge problem transformed - through composting with wood chips - into the world's largest mother lode of odor-free, almost sterile organic mulch.

It will be available at the Blue Plains sweage treatment plant off I-295, and possibly at other distribution points in the city and suburbs, and will probably be in loose piles for residents to abg or cart off for organci mulching and fertilizing of gardens.

U.S. Department of Agriculture scientists, who have been testing 60-ton-a-day sludge composting for more than three years in Beltsville, Md., have given a clean bill of health to Blue Plains' product - even for use in home gardens.

And a marketing study now being completed for the Metropolitan Washington Council of Governments has found that the peat-like compost will be so popular, whether given away free ro sold at low coust, that even in 1980 when Blue Plains alone will be producing 1,800 tons of sludge a day there will be no problem in getting rid of it.

"This is good quality sludge compost compared to otehr cities, and we've done hundreds of analyses," says Dr. James F. Parr, chief of USDA's biological waste management laboratory in Beltsville. "It's very exveptional compost for use in gardens. I use it in my flower pots and my colleagues use it in flower and vegetable gardens. I would, too, but I'm not a gardener."

The only major reservations about the use of composted sewage sludge in gardens concern the presence of heavy metals (zinc, copper, cadmium and lead) or microorganisims like salmonella, which can cause food poisoning.

The seven-week composting proces, which mixes sludge with wood chips and in which natural decay raises temperatures above 150 degrees, ills virturally all salmonella and most other bacteria, leaving the compost odorfree and almost sterile.

However, USDA soil microbiologist Dr. Wylie Burge says, "It's stell possible to lcate salmonella in low numbers from time to time in the compost, but I don't think it constitutes a hazard, and I'm not afraid to use this compost in the vegetable garden." He said there is much more danger from salmonella from letting foods sit around at room temperature or walking in a park where dogs are given free rein than from the compost.

Maryland health officials are not concerned about the rare presence of salmonella in the compost but are worried about the presence of cadmium, residures of which can build up in the body adn cause liver or kidney Damage and hypertension. However, USDA scientists, while praising Maryland's caution, say the presence of heavy meatals in Washinton sewage is exteemely low - since there are few industrial plants that pollute the area's water - and that it constitutes no threat.

A spolesman for Maryland's health department said, "We're very much in favor of this, with only one reservation, that with indiscriminate use in home vegetable gardens, especially with root crops that are eaten raw, there could be a cadmium buildup."

He left in doubt whether Maryland, whose scientists have been jointly operating the Belatsville composting project with USDA, might block free public distribution of the compost in the state, at least to homwowners. Farm and commercial use of the compost will definitely be allowed and ecvouraged, since such use can be monitored by the state.

"It would be too bad if Maryland soesn't make it available to the genreal public," said USDA's Dr. Parr. "But residential use is a small part of it . . . bulk use will account for most of the compost and the state already has approved composted sludge for golf courses, parks, road banks, nurseries and landfill acorss the state."

"And I don't agree with them at all on the cadmium. It's pretty damn low . . . 9 parts per million, and at most 14-16 ppm while Chicago's sludge has over 200 ppm and they're giving it away to everybody. I don't think they should be, but anythingleas than 25 ppm is safe'" said Dr. Parr.

"I can agree with the philosophy of being cautious, but this is good sludge, especially compared to cities lkie Baltimore, which has a hell of a bad sludge . . . it would kill hte plants you put it on because of the heavy metals in it but this should be recycled, it's high quality."

Neither city nor Vriginia officials have questioned its qualtiy, however, adn free distribution should begin as soon as the Blue Plains composting gets under way and distribution points are settled on.

Jean Levesque, director of the city's water resources management administration and an enthusiastic composter, said, "We never had nay problems getting rid of sludge form 1933 until 1969" when the suburbs had become so built up that the odoriferous raw sewage could no longer be spread on open farm fields. Blue Plains' raw sewage sludge is now buried - currently in upper Montogomery County - at great expense, although "digested" sludge, which is heat treated to reduce gas and liquid, is still used on area farms as well as for composting at Beltsville. About 50 per cent of Blue Plains' daily output of 600 tons of sludge is "raw" (not heat-treated). The advanced waste-treatment equipment now going in at Blue Plains will remove twice again as much sludge, or solid matter, form area sewage water, thus greatly improving quality of the remaining liquid dumped into the Potomac River. Blue Planins has long been the river's major polluter.

Levesque said sweage sludge has gotten such a bad name in the past few years that "we're going to have to advertise the compost in order to get rid of it. I imagine we'll come up with some catchy name but initially at least we'll have to give it away free."

The principal users of Blue Plains (the city and Montogomery and Prince Geroge's counties) are expected this spring to approve construction o f sludge incinerators at Blue Plains, in case composting isn't as wildly popular as most officials expect it to be and as backup for the composting program.

The U.S. Environmental Protection Agency had opposed early designs for the incinerators as wasteful of fuel - large quantities of juel are needed to burn wet sludge - but the new designs could burn sludge that is 60 per cent water with almost no juel at all, says Levesque," because at 60 per cent sludge will theoretically burn by itself."

But composting, recycling human waste, would still be cheaper and better environmentally, said Levesque. "We feel composting is the best way."

The marketing study done for COG by an environmental consulting firm here found in its final draft report that much of the compst would probably be used by farmers, especially since the use of chemical fertilizers in recent years has left "the organic content of farmland . . . somewhat depleted. Farmers have traditionally used organic materials such as manure, straw and husks to increase organic content of soils" but such use has dwindled.

Sewage compost, whilce generally a soil conditioner - imroving both light sandy soils and heavy, compacted soil - ti is also a low-grade fertilizer, containing about 1 per cent nitrogen, 2 per cent phosphoric acid and a trace of potash, according to USDA. Thus to provide the same nutrients as a 5-10-5 chemical fertilizer it would take 5 to10 times as much composted sludge as chemical fertilizer.

Washington's composted sludge, from the Beltsville pilot study, has already been used expensively here. The National Park Service is spreading it as mulch and soil conditioner throughout its gardens and flower beds - although in 1975 the White House balked at spreading composted sewage on the lawns just in case it was more odoriferous than advertised - and more than 9,000 tons of it was used in creating Constitution Gardens, which opened last spring beside the Reflecting Pool. Seneca Falls State Park in Montgomery County also used 9,000 tons and Beltsville has never had touble finding takers.

One hurdle to the composting plan is that Blue Plains needs 30 acres on which to put 600 tons a day of sludge in long piles for mixing and aerating and wants 17 acres of National Park Service land at Oxon Cove, where the Park Service planned to build a public gold course in 1978.

A lease is being worked out now, sunject to public hearings and an environmental impact assessment, to lend the 17 acres for five years and condense the golf course's 18 holes, with Blue Plains enlarging the course at the end of five years. The PArk Service expects some opposition to the move from Oxom Hill residents who, though they live at least a mile from the stie, may fear it would be odoriferous.

A reporter's visit to the Beltsville site found little odor, and that not unpleasant, because the "aeration" method of composting uses pipes underneath the piles to suck air into the compost and the air is then filtered.

The marketing study found marry U.S. cities already selling or giving away sweage sludge of one kind or another - some of it heat-dried and others blended - but all with "catchy" names form the famous Milorganlte, now a "household word," according to the report, to names like Chicago's "Nu-Earth," Houston's "Hou-actinite," and Los Angeles's "Nitrohumus." Milorganite is Milwaukee organic nitrogin, a sludge heat-treated to kill organisms. None of the cities mentioned abouve has as large a sludge composting operation as Washington is proposing.