The Consolidated Rail Corp. yesterday reported a loss of $84.8 million for the first quarter of 1980, an improvement over the restated loss of $125 million for the first quarter of 1979.

However, in its report on first-quarter operations, Conrail, the federally subsidized freight railroad which already has drawn nearly $2.8 billion in federal funds since its creation four years ago, painted a bleak picture for its immediate future.

Conrail's revenues for the January-March period were up 12.5 percent over the comparable 1979 period to $1.02 billion, affected favorably by general freight-rate and fuel-surcharge increases totaling about 14 percent granted to the railroads since the first quarter of 1979.The relatively mild winter weather this year also helped.

But significantly, Conrail said, carloads carried in the first quarter declined 5 percent, compared with the first quarter of 1979, and freight carloads originating on the Conrail system fell 9 percent. Motor vehicle loads were off 34 percent, and motor vehicle equipment loads were down 24 percent.

"Current traffic trends indicates a continuation, and even acceleration, of these declines as the result of economic conditions which are affecting the nation and particularly the geographic area served by Conrail," the company said yesterday. "The adverse financial impact on Conrail will be substantial in the period ahead.

Although Conrail pointed out that in each year of its existence, its losses have narrowed, the bleak financial outlook in yesterday's report is sure to intensify the debate in Congress about what to do with Conrail after the current authorization of $3.3 billion runs out.

House transportation subcommittee this week included in a railroad deregulation measure it approved a provision Chairman James J. Florio (D-N.J.) called "a supplementary protective device" to assure freight rail service in the Northeast should Conrail not survive in its present form.

The provision would increase the author of the secretary of Transportion to develop proposals for additional restructuring by transferring Conrail property to other railroads.

News services also reported the following:

General Dynamics Corp.'s chairman told shareholders yesterday that first-quarter profits rose 23 percent from last year's period to a record $36.3 million and the company should be able to withstand the nation's economic recession.

David S. Lewis, also chief executive officer of the diverse manufacturing company, said General Dynamics earned $1.33 a share on sales of $1.07 billion in the latest quarter. Those results compared with earnings of $29.5 million ($1.08) on sales of $895.6 million in the same period in 1979.

General Dynamics operates in the aerospace, marine and electronics fields and makes commercial aircraft, tactical missiles, space systems and marine equipment.

Quaker Oats Co. had a turnaround in the March quarter and earned $1.36 a share, up from $1.16 a year earlier.

For the nine months, profit was down to $3.56 a share from $3.69 a year earlier.

Net income for the quarter was $28.2 million on sales of $620.8 million compared with $24.2 million on sales of $502.1 million.

Chairman Robert D. Stuart Jr. said a 44 percent rise in domestic grocery sales, a $5.6 million pre-tax gain on foreign currency translations, better chemical sales and much improved sales of toys produced the turnaround

Nine months net was $74.2 million on sales of $1.799 billion, compared with $77.1 million a year ago on sales of $1.471 billion.