A slim and well-tanned Spiro Agnew came to the door of his seaside condominium here today and denied a published report that he had returned to the state to pay some $200,000 in back taxes.

The former vice president, who six years ago resigned from office and pleaded no contest to a federal tax evasion charge, said he had paid his back taxes to the Internal Revenue Service the same year he resigned.

These taxes were paid with the aid of a $200,000 loan from entertainer Frank Sinatra, Agnew's wife Judy said today as she rode up the elevator to the 11th floor of the English Towers condominium.

The loan, the former vice president and Maryland governor said today, is "all paid back now."

"It took four years," he added. But the IRS still claims Agnew owes the government $13,000 for using the vice-presidential aircraft on personal business and for improvements made to his Chevy Chase home at government expense in 1973.

Washington tax attorney Myron Mintz calls the government's position "outrageous."

"The man was required to use government aircraft because of his position. The Secret Service required him to make certain improvements to his home. For him to be taxed on those is to be sand-bagged," said Mintz.

Mintz said he has not seen his client since last October when they had dinner together in Palm Springs, Calif.

"He's is living a very ordinary life, very modest," said Mintz. Mintz said he does not know how Agnew is supporting himself.

In addition to his Palm Springs home, Agnew has owned a seaside condominium at the English Towers for four years, Mintz said.

The condominium, furnished in wicker furniture with a pale shag rug, has a balcony commanding a magnificent view of the sea.

The walls are decorated with reproductions of French impressionists and photographs of Agnew and various celebrities golfing. A picture of Bob Hope hangs on one wall.

Judy Agnew, who said she arrived here on June 1, said her husband had been overseas on business. Neither she nor Agnew would say where.

On the way to dinner tonight, Agnew came over to a reporter and said of the 1973 tax evasion case, "It's old news. It's five years old. I only borrowed the money [from Sinatra] to pay back the tax so I could leave the country [on business]." CAPTION: Picture, SPIRO T. AGNEW . . . IRS has $13,000 claim