The estimated $20 million owed the District government in back taxes is going to be more difficult to collect than the city might expect, according to a survey of the 10 firms the city says owe it the most in delinquent back taxes.

Of the $500,000 that the city says these businesses owe it, only a fraction is likely to be collected any time soon.

The District's finance department announced plans earlier this week to hire 20 bill collectors at a cost of $350,000 and extend operating hours to 9:30 p.m. in an attempt to track down 24,340 delinquent individual and business tax accounts.

But an examination of the "top ten" list of businesses provided by D.C. Finance Director Carolyn L. Smith showed that:

Two firms deny owing any taxes to the city.

Ownership and tax liability of three of the businesses are in doubt.

Two firms plan to pay the back taxes, but are in deep financial trouble and will seek to spread the payments over months or years.

Of the three remaining companies on Smith's list, one habitually maintains a large tax bill and its owner says he has no intention of changing his practices; the assets of another have already been attached by the District government; and officers of the last firm declined to comment.

Smith said the tax bills of the top 10 add up to more than $500,000. She said the firms owe a smorgasbord of taxes -- including sales taxes, income taxes withheld from employes, franchise taxes and property taxes on business equipment. The city has no breakdown of the various taxes each company owes, instead listing only a total for each, Smith said.

She said the top 10 firms have all owed their tax bills for "probably more than six months."

"These are the people we've tried everything with," she said. She said the city has applied for liens against the assets of all 10 companies.

She said the city has already attached the assets of one firm -- W. H. Bone, formerly a chic restaurant in Southwest Washington -- and plans to sell them to pay a delinquent tax bill of $52,839.

No officials of W. H. Bone could be reached for comment.

The biggest single delinquent, owing more than $170,000 according to Smith's figures, is Harambee House, the financially beleaguered black-owned hotel near Howard University on Georgia Avenue NW.

"There certainly are delinquent taxes," said Larry Pitsenberger, who is overseeing the sale and refinancial of Harambee House for the U.S. Commerce Department's Economic Development Administration. The federal agency currently holds the mortgage on the hotel, but is in the midst of what Pitsenberger called "ticklish negotiations" to sell the hotel to the non profit, city-funded D.C. Development Corporation.

Pitsenberger said the hotel will pay its tax bill after the sale is completed, though he said the tax payments may be spread over some length of time.

Ford and Meredith Enterprises Inc., a Southeast liquor store cited by Smith as owing $31,342, acknowledged owing a large tax bill, though owner James Meredith said he was unsure of the exact amount.

"Actually the original debt was about double what she said," Meredith said of Smith's figures. "A large part has already been repaid."

Meredith said he began whittling down the bill several months ago according to a schedule agreed upon by Smith's finance department. Smith said it was "very possible" that such an agreement had been reached, though she was unaware of it.

Two firms listed in Smith's top 10 strongly denied owing the taxes she said they owed. Joe DiCesare, owner of DiCesare and Associates -- a printing firm at 1730 K. St. NW -- said he did not owe the $37,315 cited by Smith.

"Last October I owned closer to $68,000 in sales tax for three years," DiCesare said. He declined to comment when asked why the bill had been allowed to accumulate for the three years.

DiCesare said he paid the entire $68,000 last October, "and I mortgaged my house to do it."

"Last October?" Smith said. "Well, that would have shown up by now, and we still show the delinquency.'

Smith also said that the Volpe Construction Company, one of the metropolitan area's largest, owes the city $33,435 in taxes. But a company spokesman denied owing anything.

"I'm positive of it," said Jim Cade, the company's assistant treasurer in charge of accounting duties. "About five or six months ago they sent us a letter saying we owed personal property taxes. We don't owe it. Our taxes have been filed and paid."

Cade said he was told by the finance department that the taxes -- "something in the range" of the figure cited by Smith -- dated back to 1978, and were for equipment that the company owed in the District.

"I know how much equipment we had there, and they're wrong," Cade said. He said the company heard nothing about the alleged 1978 delinquency until late in 1979, and said he had replied to the finance department that all the firm's taxes are paid.

Smith said Dyna-Lease Marketing Corp., a New York-based firm with offices in Silver Spring, owed $56,570 in taxes.

Robert Higgins, president of the company, said Smith's figures might be accurate but argued that Dyna-Lease is something of a special case. Higgins said the company, which leases photocopying equipment, "constantly has a considerable liability regarding personal property taxes."

Higgins said the company is charged the personal property tax on all the equipment it leases to other businesses in the District -- a bill that can run from $20,000 to $50,000 monthly.

"We always have something outstanding," Higgins said. "We're constantly paying this tax to the government." He said the company is never really current in its tax bills, and added that the personal property tax is eventually passed on to the firms that lease the equipment.

In three cases, firms may have gone out of business or changed hands since the information on which Smith based her list was compiled. Smith said that as far as she knows, the information in her list is current.

Smith cited a $23,194 tax bill owed by "1243-20th St. Inc. operating as The Greenery." But Richard Stewart, owner of The Greenery -- a popular restaurant at 1144, 18th St. NW -- said that "1243 20th St. Inc." became defunct two years ago.

He said that since then he has heard nothing from D.C. tax collectors about any overdue tax bill.

Smith listed a Bixby's Warehouse restaurant at 1144 18th St. NW -- said that "1243-20th St. Inc." became delinquent taxes. Again, however, a spokesman for Joe & Moe's restaurant, currently at the site, said Bixby's has been out of business for several years.

Smith also listed a Town and Country Construction, Inc. of Forestville, Md., as owing the District more than $23,000. No such firm could be located.

The final firm on Smith's list was Capitol Hill Homemaker and Health Aid Services Inc., located at 411 8th St. SE. The firm provides household help for the elderly.

Smith said the firm owes the city $28,846 in back taxes. Karen McNeil, business manager of the company, said she did not wish to comment on the firm's finances.