The House and Senate Agriculture committees, working on separate but equal tracks of political frustration, failed yesterday to break impasses over key price-support sections in their new farm bills.

An apparent Senate compromise collapsed overnight and Sen. John Melcher (D-Mont.) bluntly warned that he would block any efforts to weaken costly price-support provisions the committee adopted last week.

Melcher's warning and the committee's inability to come to an agreement led Senate Majority Leader Robert J. Dole (R-Kan.) to indicate that he will make good on an earlier threat to bypass the committee and take his own farm-bill proposal to the Senate floor today for a showdown.

"Everybody wants a little more," Dole complained yesterday. "We've lost sight of what's important -- the budget . . . . Let Melcher block it, let the Democrats block it, so the people will know who's blocking the bill."

Melcher and other Democrats, however, have insisted that they are ready to vote on the bill as it stands and are laying blame for the stalemate on Dole and committee chairman Jesse Helms (R-N.C.).

The Senate panel wrangled throughout the day, but was limited to discussing food-stamp provisions of the bill after Melcher said he would object to the committee's staying in session if attempts were made to rush through the wheat and feed grain support section.

"It is very difficult to run a committee under such circumstances," Helms said. "We've played games up and down the road. I think the message I'm getting is that we don't want no farm bill."

Melcher, however, retorted that since the panel last week passed the controversial income-support provision, "There has been backroom collaborating to see what could be done to change that vote. I just want to be prepared when it does come."

The resisters on Melcher's side include several farm-state Republicans who have refused to go along with the Dole-Helms moves to roll back farm price supports and set federal agriculture outlays closer to budget guidelines.

Political heartburn was the order of the day in the House as well. A vote to reconsider last week's approval of a price-support program was postponed until today.

The committee was to have reconsidered its adoption of a plan sponsored by Reps. Thomas S. Foley (D-Wash.) and Ron Marlenee (R-Mont.). But the idea was shelved as Foley and others attempted to hammer out an agreement that might draw less resistance and provide a more united front on the House floor, where attacks on the bill are expected.

As the negotiators negotiated, the committee spent most of National Watermelon Day, proclaimed by Agriculture Secretary John R. Block, on "miscellaneous" farm-bill amendments. One, which passed, would allow watermelon growers to vote to assess themselves for research and promotion.