Legislators from Baltimore and eastern Maryland counties joined their colleagues from the coal-rich western part of the state today and voted to repeal a ban on steep-slope coal mining, despite Gov. Harry Hughes' threat to veto the legislation.

Maryland's decade-old ban on mining of slopes steeper than 20 degrees "was unnecessary then and is unnecessary now," declared Del. Michael H. Weir (D-Baltimore County).

Weir was one of several suburban members of the House of Delegates who followed the lead of Del. W. Timothy Finan (D-Allegany) in approving the repeal by a vote of 85 to 42.

The vote came after a brief but heated debate over the repeal's environmental impact. Now the bill will be sent to the Senate, which has approved a comparable measure.

The Democratic governor, who rarely shows his hand on legislative vetos, has hinted he would kill any legislation lifting the prohibition against steep-slope mining.

In threatening the veto, Hughes said he was worried about the effects of steep-slope mining on residents and the environment of Western Maryland.

Those concerns were raised again today, this time by delegates from Montgomery and Anne Arundel counties.

"The environmental risks outweigh the possible economic advantages" of increased coal production in Allegany and Garrett counties, said Majority Leader Donald B. Robertson (D-Montgomery).

Robertson, who along with other House leaders was free to differ with Speaker Benjamin L. Cardin (D-Baltimore) on the issue because it is not part of the leadership's legislative package, voted against the repeal.

Ultimately, so did Cardin, who waited until the last seconds of voting to register his red "no" vote on the House's electronic tally board.

Finan, one of the most respected junior members of the House, fended off several critics of the repeal, saying that lifting the prohibition would have no effect on the streams and waterways in his region of the state.