As the details of Sen. Bob Packwood's tax proposal emerge, Washington's latest Paper Chase is coming to a close.

Lobbyists, lawyers, accountants and reporters have been in full cry after the tax-revision proposal, even though it is still far from final, is subject to massive rewriting by the Senate Finance Committee, is vulnerable to endless amendments on the floor of the Senate and -- if approved -- is a candidate for more changes in a House-Senate conference.

In recent days, rumors and leaks about the contents of Packwood's package have generated ulcers among the thousands of interest groups with a stake in tax overhaul. One would think that the Oregon Republican and his Finance Committee staff had been granted divine authority to rewrite the tax code, rather than mere mortal responsibility to produce a first draft for the committee's consideration.

The accounting firm of Price Waterhouse, normally a bastion of discretion, discovered firsthand the intensity of the chase when two members attended a New York speech Feb. 27 by Finance Committee chief of staff William M. Diefenderfer.

Diefenderfer mentioned some changes the Packwood plan might propose. The two accountants, following the firm's standard practice, leaped to the telephone and reported the developments to the home office. An employe there took down the information and wrote it up in memo form, for internal use.

Within hours, the memo had somehow hit the streets and appeared in lobbying offices all along K Street. By Friday afternoon, it had been given to reporters and to Finance Committee staff aides -- some of whom were surprised to learn details of the draft they were supposedly writing. The normally anonymous accountant who wrote the memo was deluged with phone calls.

Companies, associations, public-interest groups and other organizations in Washington and elsewhere are desperate to find out whether tax benefits they depend on are slated for oblivion. Their woes are compounded by the fact that the plan is being written essentially by three people -- Packwood, Diefenderfer and chief committee counsel John O. Colvin -- who aren't talking.

They sometimes reveal details in meetings with special-interest groups, in both open and closed sessions. But Packwood and his aides have proved reluctant to share those details with reporters.

Some aides to Finance Committee members who are not in on the tax developments say they are receiving 50 to 70 phone calls a day from interest groups wondering whether their oxen will be gored.

"Every beer distributor in the state is calling me because there's a rumor excise taxes will be raised," said one aide to a senator. "I told the last lobbyist who bothered me one too many times looking for secret papers that I would never return his phone calls again if he kept it up."

To the corporate tax lobbyists who have worked the halls of the Longworth House Office Building, home of the tax-writing Ways and Means Committee, and the Dirksen Building, Finance's headquarters, obtaining the Packwood plan is not merely a point of pride. "Washington reps say their corporate people can't understand why they don't have this document," said Rachelle Bernstein of the Chamber of Commerce.

Reporters writing about elements of the package are deluged by readers begging for more information.

"Your last paragraph could put me out of business," moaned real-estate broker Adam Goddard, calling about an article mentioning possible cutbacks in tax breaks for developers. "Every day they sit there and juggle with people's careers. This has caused so many heartaches."

The consensus seems to be that the stakes are higher now than when the Treasury Department was formulating President Reagan's proposal or when Ways and Means Chairman Dan Rostenkowski (D-Ill.) was drafting a bill. Because the House has passed its tax-revision bill, a tax break that survived in that measure and is not targeted in the Finance package is not likely to be curtailed. Tax benefits scaled back by the House will be even more vulnerable if the Senate goes after them.

Press reports have fed the process, raising hopes and fears among interest groups even if the reports could not be independently confirmed. The Coalition Against Double Taxation, for example, whipped out a study a few hours after Wednesday's Wall Street Journal reported that the Packwood plan might limit the deduction for state income taxes.

Such a limitation "Will Hurt Homeowners and Discriminate Against Certain States," trumpeted the title of the study. "It's a fact of life in this business," said Robert Chlopak, executive director of the coalition. "If you don't have a response when the proposal comes out, you're out of the ball game."

Packwood said in a speech to an insurance group Wednesday that about half of the information he had seen in the press was correct. Etta Fielek, Packwood's spokeswoman, said those seeking to find out about the package are shooting at a moving target, because it is continually being changed.

"My understanding is that they are holding it very tightly," she said. "Most of it [press coverage] has been inaccurate. Or if it was accurate, it was only so for a brief moment."