Anyone wondering about the impact of the Gramm-Rudman-Hollings budget-balancing law need only place a telephone call to the Federal Election Commission.

While the FEC has never been especially popular with the 535 lawmakers who are subject to its audits and investigations, it has been a treasure trove of information for reporters, interest groups and rival politicians trying to track the flow of campaign cash to congressional candidates. In response to requests for lists of contributors, the agency has always made available reams of computer printouts, usually within hours.

As of yesterday, however, every caller was read a prepared statement warning that requests will now take several working days, and that some services will be eliminated, "because of the Gramm-Rudman budget cuts." The service cutbacks are to be officially approved at a commission meeting today.

"It's not good," said FEC spokesman Sharon Snyder. "If Gramm-Rudman continues, say goodbye to most everything."

The FEC is hardly alone in reacting to the deficit-reduction act, which has cast a lengthening shadow over official Washington. Programs ranging from juvenile justice grants to urban development action grants have been frozen while federal agencies try to adjust to the 4.3 percent cutbacks that will take effect March 1, with more to come over the next five years.

The commission will lose 25 percent of its computer capacity on March 1, Snyder said. It will no longer be able to use its high-speed computer printers to churn out hundreds of requests overnight, and must rely instead on slower machines during working hours.

That's not the worst of it. Gone from the computer files will be all the congressional campaign records from 1976 to 1982. Gone, too, will be lists of individual contributors to congressional candidates, as well as loans to campaigns and transfers from political action committees (PACs).

Anyone seeking this information will have to trudge over to the commission's office -- it's moving from K Street to 999 E St. NW -- and look it up manually on microfilm.

The computer system will still spit out all donations made by the thousands of PACs, an increasingly important measure of special-interest influence. But this will be recorded through a slower, less sophisticated system that will be more prone to error, Snyder said.

The commission is suffering a double blow because of the budget-balancing law and a cutback in its appropriation. Snyder said that together, these changes will reduce its $12.8 million budget by nearly $1 million.

The 237-person staff will not be cut because the commission "never recovered" from its layoff of employes early in President Reagan's first term, Snyder said.

The reductions will be felt most sharply in the weeks before the November elections, when the FEC usually extends its working hours to accommodate the hordes of journalists -- and political opponents -- who pore over contributor records in search of damaging material.