Consolidated Rail Corp. yesterday began posting notices that it will cease service over the Virginia segment of Delmarva Peninsula rail lines, including a ferry service across Chesapeake Bay between Cape Charles and Norfolk, after April 1.

The Philadelphia-based railroad's decision came after the Accomac-Northhampton transportation district commission said it could not afford the costs being assessed by the new Northeast railroad, set up last year to take over major operations from bankrupt companies.

Instead, Virginia officials are seeking to reach an agreement with an independent railroad operator, to continue service over the line from Pokomoke City, Md., to Norfolk.

ConRail spokesmen said yesterday their decision to cancel service when total federal subsidies expire after April 1 leaves open the possibility of exchanging freight cars with a new carrier - if such an independent operator is created. In such an event, through service would be maintained.

Under federal legislation establishing ConRail, the federal government agreed to help subsidize unprofitable branch lines not taken over by ConRail.

Under Virginia law, the state is barred from paying any share of such a subsidy and local groups would have to pay more in the coming year to ConRail. According to Virginia officials, ConRail asked for an increase in the amount of subsidy for the coming year of $250,000 for a total of $1.2 million - too much for the local groups to bear.