The archbishop of Baltimore today called on Maryland legislators to reject a proposal by Gov. Harry Hughes to ease the state's restrictions on the public funding of abortions for poor women, signaling a more aggressive posture by the Catholic Church in legislative affairs.

Archbishop William Borders, in a speech read by his auxiliary bishop because Borders was ill, urged about two dozen legislators attending the archdiocese's annual legislative breakfast to "defend the rights of the unborn against what we sincerely believe is unjust aggression."

Although Borders frequently has used the same forum to deliver that message in past years, his speech today comes as the General Assembly prepares for what could be one of its more bruising battles on the abortion issue and at a time when the Maryland Catholic Conference is raising its profile in Annapolis.

"Let's just say the archbishop can count votes, too," said one Baltimore legislator after listening to Borders' message, a reminder that the same abortion guidelines proposed by Hughes this year were approved by the House of Delegates last year. A Senate committee refused to go along with the change.

That House action has persuaded proponents of the more liberal abortion funding rules that such changes have a chance for passage for the first time in five years.

It is also one factor in the church's decision to beef up its presence during the 1985 legislative session. With a new executive director and a permanent office here, the Catholic Conference -- the policy-making body for the archdioceses of Washington, Baltimore and Wilmington -- is seeking a higher profile and intends to play a more direct role in lobbying the legislature on the abortion issue as well as questions of increasing welfare payments and abolishing the death penalty.

One of the legislators who will lead the fight against relaxing the abortion funding, Del. Timothy F. Maloney (D-Prince George's), said, "There's a feeling that the church, not just on abortion but on a whole range of social issues, has not been as strong as it should."

The legislators advocating abortion rights are seeking the change in state funding rules because they say the current guidelines, in effect since 1980, have cut publicly funded abortions by one-half by requiring physicians to certify in writing that a woman would suffer mental harm if she does not obtain an abortion. The guidelines proposed by Hughes remove the requirement for written certification and substantially ease the mental health criteria for obtaining publicly funded abortions.