Congress saw the tip of the Gramm-Rudman-Hollings iceberg when it returned to town last week. It also found that most of the lifeboats were missing.

Initial spending cuts from the new budget-balancing law were taking effect, and there were no early signs of an accord with the White House to prevent even more drastic cuts just before the November congressional elections.

Lawmakers' offices reported they were getting hundreds of letters and phone calls from angry government retirees who had found that pension cost-of-living increases due on Jan. 1 were being withheld as part of the first wave of cutbacks.

And members themselves faced cutbacks of $62 million in their office staffing and expense accounts that could lead to personnel reductions, pay cuts for employes and supply shortages.

"Now they're staring it right in the face . . . and they're asking, 'Isn't there something we can do?' " said Rep. Vic Fazio (D-Calif.), who, as chairman of the House appropriations subcommittee for the legislative branch, was under siege from his colleagues.

In just one hour on the House floor during a debate Thursday, Fazio had been accosted by about 25 of his colleagues with tales of woe, not unlike the complaints that lawmakers normally hear from constituents.

"They didn't think it would happen to them . . . But we have to suffer like everyone else," said Fazio.

What alarmed many lawmakers even more than the first wave was what lies ahead: much bigger cuts next fall if Congress and President Reagan fail to reach agreement on alternative deficit reductions in the meantime.

On this score, the outlook was even bleaker.

Congressional leaders of both parties put out feelers for tax increases and balanced cutbacks in defense and domestic spending, with some even mentioning the unmentionable -- Social Security reductions as part of a long-term solution.

But Reagan, in several sessions with Republican congressional leaders, continued to hold the line against tax increases and to demand defense spending increases and domestic spending cuts that have been unacceptable to Congress in previous years.

His fiscal 1987 budget, scheduled for submission to Congress early next month, would be kept alive only as a "vehicle of repudiation," according to Senate Budget Committee Chairman Pete V. Domenici (R-N.M.). Democrats were already ridiculing his "privatization" proposals as a "fire sale" of the nation's assets; Republicans preferred to ignore the subject entirely.

Republicans as well as Democrats talked this week of a "grand compromise" with the White House emerging if the stalemate deepens. But some worried that early intransigence for bargaining purposes could make it harder to agree on fiscal 1987 cutbacks of $60 billion or more, five times the $11.7 billion cutback already required for the rest of fiscal 1986.

Congressional budget experts testified that a $60 billion cut would translate into cuts of 18 percent for defense and 25 percent for domestic programs. "In other words," said Rep. Silvio O. Conte (R-Mass.), ranking Republican on the House Appropriations Committee, "we ain't felt nothing yet."

The Gramm-Rudman-Hollings bill seeks to force agreement on a deficit-cutting strategy by threatening huge automatic spending cuts over the next five years if specific annual deficit targets are not met.

The cuts would halt Reagan's five-year military buildup and devastate domestic spending programs, theoretically providing a mutual incentive for compromise.

The initial automatic cut of $11.7 billion for fiscal 1986, which takes effect March 1 unless Congress unexpectedly agrees to an alternative in the meantime, would leave this year's deficit at more than $200 billion under current projections. A cut of about $60 billion -- Domenici says it could go as high as $70 billion -- would be required for fiscal 1987 in order to meet the $144 billion deficit target the law establishes for next year. Subsequent reductions would reduce the deficit to zero by fiscal 1991.

The fiscal 1987 cutbacks would take effect Oct. 15, just one month before congressional elections in which continued Republican control of the Senate is at stake -- a timetable that provides ample opportunity for political brinksmanship. Lawmakers have warned Reagan that agreement on an alternative deficit-reduction plan, if there is to be one, would have to come by midsummer to avoid what Sen. Lawton Chiles (D-Fla.) has called the "guillotine" of automatic cutbacks.

With the initial impact of the law being felt only by military and civilian retirees of the government, most lawmakers interviewed last week said the effect of the impending budget squeeze has yet to be felt in the country.

"They don't know what Gramm-Rudman is," said Sen. Daniel Patrick Moynihan (D-N.Y.). "Most of the country is really not aware of the implications -- much less most of Congress," said Rep. Leon E. Panetta (D-Calif.).

But university presidents and other education lobbyists are beginning to mobilize, as well as retirees' groups that are pushing for reinstatment of the inflation adjustments for government pensions.

Congressional leaders are counting on the pressure to build as more and more constituency groups become aware of what is in store for them under the second round of cuts. Only after the pressure hits a critical point is real movement likely, they say.

A visit last week from a delegation of mayors indicated that moment may still be a long way off. The mayors were pleading for continuation of revenue sharing for local governments, a battle that was fought and lost last year. "If they think their problem is losing revenue sharing, do they ever have a surprise," said a congressional aide.