A House-Senate conference committee agreed yesterday on a compromise plan to pare government regulation from the nation's railroad industry -- the last of three major deregulation bills proposed by the Carter administration.

The prompt action by the negotiators paves the way for final passage of the measure next week, in time to send the bill to the president's desk before Congress leaves for its pre-election recess.

The compromise essentially follows the more liberal House version of the bill, which allows railroads to raise freight rates sharply without review by the Interstate Commerce Commission, even if they dominate a particular market.

The ICC would not be allowed to intervene until the rate increases exceeded 160 percent of a railroad's out-of-pocket costs of transporting freight. This "threshhold" would rise gradually, to 175 percent of costs by 1984.

The agreement yesterday marked a victory for the Carter administration, which has been lobbying intensely for the measure as part of its long-range strategy of ending regulations that it says are inflationary.

Transportation Secretary Neil Goldschmidt said after yesterday's action he was "delighted" with the conferees' action, and expressed hope that the two houses would act speedily on the final bill.

Goldschmidt said in a statement the legislation "will benefit the consumer, the shipper and the rail industry" and would "provide the flexibility in rates that the railroads need . . . ."

The most sweeping of the three bills enacted in late 1978, deregulated the nation's airline industry. A second bill, involving the trucking industry, was signed into law last July.

The administration had argued for enactment of all three measures as a way to heighten competition in the transportation industry. Critics had blamed over-regulation by the government for lackluster performance and high fares.

Deregulation of the nation's airlines has been widely hailed as a success. Although airlines recently raised fares to cover soaring fuel costs, the initial impact of the legislation was to lower prices and broaden services.

The "threshhold" figures agreed opon yesterday would apply to increases over and above a 6 percent rate increase that would be allowed as an inflation adjustment, no matter what a railroad's out-of-pocket costs.

The compromise also includes other provisions that would make it easier for a railroad to raise rates unilaterally on its portion of joint-line shipments, to abandon marginal tracts and to sign contracts with customers.

The conferees also agreed to authorize another $329 million for the federally financed Consolidated Rail Corporation, which is expected to use up its existing government funds sometime next spring.

And they voted to provide another $600 million in low-interest federal loans over the next two years to help pay for railroad rehabilitation and restructuring projects.

The agreement yesterday followed months of wrangling in both houses, including a month-long delay in the House during which opponents of the measure nearly suceeded in killing it.

Rep. James J. Florio (D-N.J.), chief House sponsor of the bill, and Sen. Howard Cannon (D-Nev.), its floor manager in the Senate, both hailed the compromise proposal.

And Eckhardt (D-Texas), who had opposed the bill in the House on grounds that it would not adequately protect shippers, also expressed satisfaction with yesterday's pact.

Passage of the bill in the House was by an overwhelming 337 to 20.