In Orlando, Fla., last Jan. 8, the cochairmen of the Committee for a Responsible Federal Budget opened a symposium with the observation that "our political leaders will move deficit reduction to the top of the fiscal policy agenda when the American people are convinced they should do so."

Nine months later, Wall Street, if not Main Street, has become convinced, and Congress and the White House are struggling with spending, taxes and the deficit.

As official Washington grappled with prospects for an arms-control treaty and a new Supreme Court nomination, the leadership of Congress and senior Reagan administration officials spent much of their time closeted in an ornate room just off the Senate chamber talking about ways to reduce the deficit.

There is almost a palpable feeling in Congress this week that the wild gyrations on Wall Street have created an unusual opportunity that must be seized.

"There's an old saying," said Rep. Henry J. Hyde (R-Ill.), "we don't read the handwriting on the wall until our backs are against the wall."

But progress on the deficit was excruciatingly slow, casting doubt on the sincere declarations that Congress and the Reagan administration were willing under the pressure of events to put aside partisan differences.

Yesterday, for example, lawmakers and administration officials were somewhat grim-faced as they emerged from another all-day session of discussing options for raising revenues and cutting expenditures to reduce the fiscal 1988 deficit by at least $23 billion.

"We're still in business; everyone is still working," said Sen. Pete V. Domenici (R-N.M.).

"We don't have a package yet, but we are progressing . . . " added Sen. J. Bennett Johnston (D-La.). "We've got a ways to go yet."

White House chief of staff Howard H. Baker Jr. was even more reticent. "We're talking about the right things," he said.

Underneath those cautious statements was some progress, however.

The negotiators are nearing an accord on a "modified" spending freeze that could save about $6 billion, fairly evenly split among defense and domestic programs. In addition, they are discussing ways to save another $5 billion to $10 billion from entitlement programs such as Medicare and agricultural aid.

That would leave them facing the need for $10 billion to $12 billion in taxes.

Meanwhile, six Cabinet members, including Treasury Secretary James A. Baker III and U.S. Trade Representative Clayton Yeutter, sent a letter to congressional leaders yesterday proposing a bipartisan effort on trade similar to the one under way on the deficit.

Asserting that the administration needs legislation that includes authority to negotiate a new global round of trade talks along with other trade issues, the Cabinet members pledged White House support for a "forward-looking . . . strong, responsible" trade bill.

The letter came to Capitol Hill just two days after Labor Secretary William E. Brock told Congress that it should not pass trade legislation this year to avoid causing panic in global financial markets.

Brock, a former U.S. trade representative, was one of the six Cabinet members who signed yesterday's letter.

Republicans and Democrats alike see considerable hope that out of Wall Street's plunge will come a budget agreement that will satisfy both a president reluctant to accept higher taxes and a Democratic Congress resistant to further cuts in spending.

"It's the best opportunity in the five years I've been here," said Rep. Timothy J. Penny (D-Minn.), one of a number of moderate Democrats who have been pressing for greater spending restraint this year. "Wall Street is the best pressure we can have."

Hyde compares the current mood in Congress to that which swept the country in the wake of California's adoption of the Proposition 13 tax-cutting measure. Wall Street's misfortunes, he said, "have sent a wave of responsibility" through the Congress.

"This looming crisis has also presented us with an opportunity to take substantial positive steps that will have a lasting healing effect on our economy," added Senate Republican leader Robert J. Dole (Kan.).

For those like Rep. Buddy MacKay (D-Fla.), who have been trying to engineer a fiscal crisis all year in order to force a "grand compromise" on the budget, Wall Street's troubles have arrived in the nick of time.

"Without the market crash we weren't getting anywhere," MacKay said. "The man on the street now understands the deficit and what's at stake. It's easier to sell tough solutions."

At the moment, however, that mood of opportunity and optimism is suffering something of a downturn.

On Thursday night, House Democrats and Republicans joined in a legislative street fight over a $12 billion tax bill that passed by just one vote and left bitterness on both sides.

House Minority Whip Trent Lott (R-Miss.), one of the lawmakers on the budget negotiating team, said the floor struggle had left him "so mad at {Speaker} Jim Wright and {Majority Leader} Tom Foley I don't want to talk to them, let alone negotiate."

Whether that hangover persists will depend to a large extent on the budget negotiations that resume this morning.

In the meantime, a growing number of lawmakers are pressing for deeper cuts than the $23 billion target that would be achieved automatically in any case under the balanced-budget law.