Shortly after Robert W. Merry became managing editor of Congressional Quarterly Weekly Report last May, he wrote a letter to a prominent Washington reporter to complain about not getting any credit in one of the journalist's stories.

"I can't help noticing how much your lovely prose rises to the level of my own sterling reporters . . . ," Merry chided gently. "Keep it up, and you may one day be eligible for consideration as a CQ writer."

The reporter, Merry explained, was one of those who occasionally fall over the line between using the Congressional Quarterly as background for their stories and stealing from it. And Merry felt his staff deserved more notice for their work because the big-time journalist had borrowed two full paragraphs from the Quarterly's story.

But the reason that Merry's letter was not more irate in tone is that part of the mission of CQ -- which is what most people call Congressional Quarterly Inc.'s Weekly Report -- is to be used by journalists whose companies pay more than $900 a year for the service.

Asked about how journalists use the CQ Weekly Report, one former Hill reporter joked: "You mean the cheat sheet?"

Founded in 1945 by Nelson and Henrietta Poynter, who were owners of the St. Petersburg (Fla.) Times, CQ's weekly wrap-up is a yeoman publication with no color photos and no fancy headlines. The latest edition, for example, is a guide to the presidential nominating process that may be as interesting as a telephone book to most people but is already locked away in most political reporters' desks as valuable property.

Past editions have dealt with issues such as whether a new index is needed for inflation, an article on damage compensation in case of a nuclear accident and the details of catastrophic insurance plans. It may not sell at the grocery checkout, but when a reporter is suddenly assigned to cover the trade bill as it heads for conference committee, the first move is to page 1633 in CQ's July 25 edition.

This is not to say that CQ is the only source for reporters covering Congress. National Journal is often tapped for larger background pieces that stretch beyond the boundaries of Capitol Hill. Journalists who cover issues for a number of newsletters often serve as on-site experts sharing their expertise with other reporters.

The Democratic Study Group puts out nothing-but-the-facts outlines of what happens on the floors of both houses. The wire services provide running explanations of what bill passes which house.

And, of course, there are always the original sources. Most senators and House members can spot a reporter's notebook at 50 yards and have their remarks polished and ready for publication. Committee aides are mostly willing to help out -- most often anonymously -- with what happened behind the scenes.

But when the editor asks the Capitol Hill reporter for an in-depth unscrambling of a mess of amendments and riders -- to be written in the next 45 minutes -- the reporter makes a quick dash to the large green binders that store past editions of CQ.

"Everybody there relies on it pretty heavily, especially when you're hit with action on a bill that you know absolutely nothing about," said Los Angeles Times reporter Karen Tumulty, who has been covering Congress for four years.

Other reporters agreed, but some said they feared that beyond the nuts and bolts of Congress, CQ often is too narrowly confined.

"Sometimes I question whether it's a really balanced view of things when so much of what is going on here on the Hill is because of what is going on at the White House or in the agencies," said George Lobsenz of United Press International.

John Fox Sullivan, publisher of the National Journal, which was formed in 1969 to compete with CQ, said the Journal has expanded its coverage beyond Congress to answer that need.

"I have tried to move away from being just a reference publication into something that people actually open up every week when they get it," Sullivan said.

But even Sullivan, whose publication has 5,000 subscribers compared with CQ's 9,000, said the Weekly Report "is terrific at being comprehensive, covering everything taking place in Congress."

Subscribers to CQ's weekly offering also can call Congressional Quarterly's research department for information. Most of the calls asking for expertise on congressional doings are from print or broadcast journalists.

The latest analysis shows that during the week of June 30 to July 17, for example, of approximately 165 queries, 46 were from newspapers and other publications and 14 from broadcasting. The remainder of requests came from 17 other categories, which included libraries (two), think tanks (three) and congressional offices (13).

Most of the news organizations that use the service, however, borrow from it anonymously, the way they consult Webster's dictionary without crediting it for every correctly spelled word.

"They're not paying for a magazine," said Peter Harkness, who was executive editor of CQ until 1986 and who is starting a new CQ magazine for state and local news. "They're paying for a service."

Perhaps the one who got the most out of the service, Harkness said, was the late Chet Huntley, who had a regular NBC radio show that was supposed to give Huntley's view of what was happening on the Hill.

"Every day we would have Chet Huntley's perspective on the news," said Harkness, laughing, "and it would be a word-for-word read of the CQ's news service."