Sen. Patrick T. Welsh had just retired to the Senate lounge for a cigarette after supporting a motion to postpone consideration of the D.C. voting rights amendment when a labor lobbyist collared him.

"I guess he was a little upset with me," said Welsh, a freshman Democratic senator from a strong labor district of Baltimore County. "He wanted to know what I was doing, what I thought. They're [labor] fighting this one as hard as they've fought any of their biggies."

For the past two days -- while Senate opponents of the controversial amendment have successfully delayed a vote on the issue -- supporters of the measure, led by labor, have fought back with equal intensity in the mahogany Senate lounge, State House hallways and offices.

Senators who received labor support in last fall's election have been hit the hardest, besieged with mailgrams, letters and telephone calls from union officials in their districts. Their every action on the floor is closely watched by state labor lobbyists.

The lobbying pressures became so intense today that Sen. Howard Denis, a Montgomery County Republican who is opposed to the amendment, asked the Senate president to have labor officials stop "roaming the hallway and pulling people off the floor while we're debating."

For Denis and fellow Republicans, the motives of labor are clear. If Maryland and 37 other states ratify the constitutional amendment giving the District of Columbia full representation in Congress, prolabor and Democratic officials will surely be elected.

"The only reason this has gotten so far," Denis said, "is that big labor wants to have people in the U.S. Senate and House of Representatives even if they have to break the Constitution in half."

Although labor has been the most visible lobbying force in favor of the amendment, it is not alone. Working more quietly behind the scenes is an organization with at least as much clout in Maryland -- the Catholic church, led by the Archdiocese of Washington.

Several Catholic senators say they have been contacted by representatives of the archdiocese in recent days and asked to support the measure. One such call was placed to Sen. Thomas V. (Mike) Miller (D-Prince George's) in the Senate lounge today.

"It was a sweet, gentle voice of a lady," Miller, who opposes ratification, said after the call. "It was the kind of voice that reminded you of a nun."

Opponents of the amendment -- who represent a large minority bloc, according to most vote counts -- say the pressures from labor and the church carry more weight than political pressures exerted by their colleagues in the Senate.

Those political pressures gained some momentum today, however, when Gov. Harry R. Hughes, who has withheld his opinion on the voting rights amendment heretofore, issued a statement supporting ratification of the measure.

A press release distributed by the governor's spokesman said Hughes "was most persuaded by the human rights aspects of the question. Historically, residents of the capital city have been denied one of the most fundamental rights of any American citizen -- the right of full participation in their government."