Senate leaders, faced with the imminent threat that government checks could start bouncing, said early today after nearly 15 hours of testy confrontation they were "fairly close" to agreement on a plan to pass a stopgap extension of the government's borrowing authority by tonight.

All day and through the night, Republicans and Democrats remained deadlocked in efforts to cut a deal under which a short-term, debt-ceiling extension could be passed in conjunction with a vote on broad GOP-sponsored legislation to balance the budget by 1991.

As exhaustion set in after parliamentary maneuvers produced only stalemate, senators attempted to work out a timetable on voting that was aimed at avoiding major financial disruptions resulting from a temporary government default.

Shortly after 2:30 a.m., Majority Leader Robert J. Dole (R-Kan.) said they were "fairly close to an overall agreement" but had hit a "little snag" on wording of the interim debt-measure, which he said they hoped to work out today. Earlier, they had talked of extending borrowing authority through Oct. 17.

Senate approval of the balanced-budget plan in conjunction with the debt-ceiling measure would send the plan to conference with the House, where opposition is mounting to provisions of the bill, despite support for some type of balanced-budget legislation. Details on Page A4.

In the absence of an accord to vote on the debt extension, Dole (R-Kan.) had warned earlier that a vote on the short-term debt measure might occur too late to satisfy the Treasury Department, which scheduled an auction of Treasury bills at 12:30 p.m. today to raise $5 billion to keep the government's line of credit open.

Even before the deal was struck, there were suggestions from administration and congressional sources that ways would be found to avoid serious financial disruptions.

Several senators, including Republicans, voiced skepticism about the administration's threats of an unprecedented default on government obligations unless the debt bill is passed today. "There is no calamity," said Sen. Steve Symms (R-Idaho), accusing the Treasury Department of "scare tactics."

"It makes you suspicious, doesn't it?" said Sen. Thad Cochran (R-Miss.) in reference to escape hatches under which the government could tap other funds or shuffle money to avoid default.

The negotiations between Dole and Minority Leader Robert C. Byrd (D-W.Va.) were conducted under heavy pressure from the administration, including a letter from Acting Treasury Secretary Richard G. Darman, warning that the government will run out of cash today.

The extension is needed because the government has hit its current borrowing ceiling of $1.824 trillion. The debt bill to which the balanced-budget provisions are attached would raise the ceiling to $2.078 trillion, enough to last a year. The short-term extension would add enough borrowing authority to last about a week or so while the Senate, which is expected to pass the budget plan, negotiates over its provisions with the House.

In his letter, Darman took note of the Treasury Department action planned for today and said the government "should be able to manage payments so as to avoid a default" so long as there was "anticipation of action that would allow us to proceed with this financing."

He did not elaborate, but Senate leaders were aiming, at the least, for a firm agreement that would point to passage of the debt measure by today.

Through most of the day, Democrats were pushing for passage of the debt measure before action on the balanced-budget plan, while Republicans, seeking to use the "must" debt legislation to force deficit reductions, were holding out for action first on the budget provisions.

Shortly before midnight, Byrd offered to vote on both proposals Thursday, prompting an angry complaint from Dole that Senate Democrats were engaged in a "flat-out stall." The budget proposal, sponsored by Sens. Phil Gramm (R-Tex.), Warren B. Rudman (R-N.H.) and Ernest F. Hollings (D-S.C.), would mandate that the president cut spending in accord with congressional guidelines if deficit limits are breached. These limits are aimed at reducing the deficit from $180 billion to zero by fiscal 1991.

Senate Democrats have a somewhat different proposal that limits presidential budget-cutting authority and allows tax increases as well as spending cuts to bring deficits within the prescribed limits.

In an escalation of political fighting over the proposals, Democrats accused the GOP of putting the 1986 or 1987 deficit limits well above deficit levels that are anticipated to protect GOP senators up for election next year from the political pain of spending cuts.