Legislative efforts to restructure the Government Printing Office have left private printers unhappy with a bill that they maintain is ambiguous, disruptive and unnecessary.

In the D.C. area alone, some 300 printing companies comprising the largest manufacturing industry here handle $66 million, or 21 percent, of the GPO's $322 million commercial contracts.

Now they fear that revisions in an 84-year-old printing law could alter the process of obtaining some of that lucrative federal contracting.

The GPO prints, binds and distributes such materials as the Congressional Record for the three government branches. Any overload work is contracted out from a bidders list of 6,000 commercial printers.

The Joint Committee on Printing, which sets policy, also oversees some 300 federal agency, in-house printing plants.

Operating with an annual budget of about $600 million, the GPO handles some 26,000 publications titles and is recognized as ad advanced, highly mechanized operation.

In recent years, however, it has been heavily criticized for delays in the printing, delivery and contracting of jobs, lack of control and monitoring of its operation, waste, poor accounting methods and duplication of materials.

In a recent evaluation by Coopers & Lybrand prising the agency for bringing most of those problems under control, the accountants still recommended that the GPO tighten its management, organization and operational practices.

Some legislators believe it is time to overhaul parts of Title 44 - the printing code - and are calling for several revisions under the Public Printing Reorganization Act of 1979.

The Joint Committee on Printing would be replaced by a presidentially appointed, seven-member board of directors to set policy and regulate the agency.

- The act would make the GPO an independent agency instead of an arm of the legislative branch, with congressional printing falling under the jurisdiction of the House Administration and Senate Rules committees.

- The position of public printer would be diluted by making it an appointed post as general manager, a position that is shared with the superintendent of documents.

According to sponsors of the bill, revamping the GPO will improve public access to government documents by improving management and by streamlining government printing and distribution. Moreover, it will cut costs, they maintain.

The printing and distribution of government publications is a costly, yet often poorly monitored portion of the bureaucratic process.

An ad hoc advisory committee estimated that the GPO's main production department, six regional plants and 14 procurement offices produced $180 million of government printing in fiscal 1978.

That's about 11.5 percent of an estimated total of $1.5 billion spent for federal printing and duplicating expenditures. And of that whopping figure, only one-third is accounted for by GPO facilities.

Now private printers want some safeguards in the bill to clarify existing ambiguities and to keep some of the attractive contract letting from being squeezed during any reorganization.

Apparent weakening of the position of public printer, confusion in the procurement process and the possibility of excluding small businesses are some of the points they raise.

"We've been assured that there will be no change in procuring contracts," said John Grant, director of government affairs for Printing Industries of America Inc. "But it's unclear from the bill who has contracting authority."

Grant, representing one of the groups that testified during recent hearings before the Senate Rules and House Administration committees, said his 8,700-member printing trade group is mostly apprehensive about "vague language" in the bill.

Another concern is the large amount of printing done by the 300 in-house printing plants in federal agencies. Grant maintains these plants are "inefficient and unecomonical."