Metro board members again postponed a decision on the proposed April fare increase yesterday, after four hours of debate and private caucusing failed to break a deadlock over what to charge for rush-hour train rides.

The deferral could delay implementation of the new fares two weeks past the board's original April 2 target, giving riders a reprieve but forcing area governments to make up the extra $250,000 per week that the financially pressed system would have collected.

"I'm sorry to see we're giving away another quarter of a million dollars because we're not able to work out the fine-tuning and details," said Virginia board member John Milliken of Virginia. Other board members expressed similar concern.

Members have agreed to increase most bus fares to 75 cents and raise some fees for crossing bus zones. But they remain divided on an issue that has tried the unity of Metro's eight member jurisdictions since the system's inception--whether short-distance rail riders should subsidize long-distance riders or vice versa.

As in past years Maryland, which wants cheap long-distance rates because its residents tend to take longer rides, is pitted against the District.

The city, with people making shorter trips, wants high long-distance fares. Virginia stands in between.

The sides are less prone to compromise this year than in the past. The D.C. and Prince George's County governments face acute pressure to economize. Montgomery County, looking ahead to the planned 1984 opening of the Red Line to Shady Grove, the system's longest segment, wants to avoid a precedent of high fares for long-distance rides.

Other big-city transit systems such as those in San Francisco and Chicago are spared similar debates either because they have a single fare for all riders or because local governments do not pay subsidies from their own tax funds. Instead, special sales taxes dedicated to transit automatically generate the money. Proposals to enact similar taxes here have failed.

Though it may break down as negotiations continue, there is basic agreement to raise the base rail fare from 65 to 75 cents. Disagreement hinges on the rail mileage fee, which rush-hour riders pay after three miles of travel. It is now 13 cents. Maryland wants to keep it at that level, arguing ridership will suffer, while D.C. wants it to rise to 15 cents, as the Metro staff has recommended.

Efforts to compromise at 14 cents have not succeeded. The distinction is not small, because each cent added to the fee reaps Metro about $800,000 annually, reducing by the same amount the money local governments must pay to support the system.

Board members had hoped, but failed, to reach a final decision last Thursday, the last day that would provide enough time for fare gates to be reprogrammed by April 2. Convening again yesterday, they discussed but could not agree on a variety of steps that would mollify various parties but further complicate Metro's already complex fare structure. Those included:

* Accepting the 15-cent mileage fee, with a pledge that no fare would be higher than $2.25, the cost of a one-way ride between New Carrollton and National Airport. This was meant to mollify Maryland.

* Sharing among all the jurisdictions a special $250,000 subsidy now paid by D.C. alone that cuts fares at the Benning Road, Minnesota Avenue and Deanwood stations by 10 cents. The plan, supported reluctantly by some Maryland and Virginia members, would have had suburban taxpayers bankrolling a special break to the city's poor.

* Setting the mileage fee at 14 cents, but requiring jurisdictions to make up in subsidies what their riders would have paid had the rate been 15 cents. That would hit Maryland hard.