The Reagan administration and key Senate members have reached agreement on the timing and way in which Conrail, the federally subsidized freight railroad, will be sold to the private sector, Senate Commerce Committee Chairman Bob Packwood (R-Ore.) said last night.

According to Packwood, the plan includes these major provisions:

The government can sell the 17,000, 17-state freight system after June 1, 1982, but only in one piece.

If Conrail is not sold in the following six months, a new element is added. If the railroad has begun to be profitable by Dec. 1, 1982, the government can continue to try to sell it only as a single entity. However, if it has not become profitable by the time, the government can proceed with the sale of Conrail in a package composed of several lines to different buyers.

After Aug. 1, 1983, the government can dispose of Conrail's assets as a single entity or in a package of several lines to different buyers.

The argument was worked out by Packwood and Transportation Secretary Drew Lewis, with the involvement of surface transportation subcommittee Chairman John Danforth (R-Mo.), and it has received bipartisan backing from a majority of the committee, including ranking minority member Howard Cannon (D-Nev.).

Besides the sale schedule, Packwood said the agreement contains a number of incentives and concessions to make Con rail "an attractive and affordable purchase." It also contains an assurance of adequate funding to guarantee essential service while the transfers are taking place.

Conrail, formally Consolidated Rail Corp., was created in 1976 out of the Penn Central and six other bankrupt railroads to preserve freight rail service in the Northeast and Midwest. Conrail's total cost to taxpayers already has exceeded $6 billion.

It has been Lewis' position that Conrail never could be profitable and that its freight assets should be sold to private railroads once they were made more attractive by federal legislative action to solve some of Conrail's current problems, a process he said would take a year or more.

These remedial steps included separating its commuter operations from its commuter operations from its freight functions because no freight road wants the commuter runs, reforming its costly labor protection provisions, and restructuring rall operating responsibilities in the Northeast so that other railroads using terminals accept a greater share of their operating costs.

The agreement contains new legislation and funding to take care of some of these problems. For instance, another $400 million for labor protection expenses would be authorized and Conrail would be able to buy out employes, up to a $25,000 ceiling depending on their tenure, and abolish the positions they held.

The agreement also includes some incentives for potential buyers. For example, up to 12 months of labor-protection expenses that acquiring railroads are subject to could be credited against the purchase price of the property. Credits for the purchasers' expenses for the negotiation and transfer also are provided if they enter into negotiations within six months of enactment of the plan into law.

The law agreement also would give Congress an opportunity within 120 days to disapprove a proposed sale of Conrail with a veto by both houses.

In order to determine whether Conrail is profitable by Dec. 1, 1982, the agreement establishes a review committee, composed of the secretaries of Transportation and Treasury, the chairman of the United States Railway Association, the Comptroller General and the chief executive officer of Conrail. Their finding must be based on Conrail's ability to generate revenues at least equal to its day-to-date operating and maintenance expenses as well as the ability to generate capital from the private money market.