Political leaders of the District of Columbia came nearly 900 miles here to discover that they have trouble in their own backyard on their drive for ratification of the D.C. voting rights amendment.

In general they got a sympathetic reaction to their campaign among delegates at the Democratic midterm convention here. They decided not to try to compete with flashy badges and ribbons worn by supporters of other causes -- principally in behalf of the Equal Rights Amendment, abortion and gay rights -- because there was simply too much competition.

However, the person assigned to lobby the Maryland delegation, Richard W. Clark of Common Cause, got a cool reception from one of the most liberal members of the Maryland legislatue, Del. Lucille Maurer of Montgomery County.

Maurer told Clark that two issues imperil her support of ratification, the possibility that it would hasten a commuter tax and recent activities of the District government concerning sewage treatment.

Maryland Acting Gov. Blair Lee III predicted that the amendment "will not have an easy time of it" when the Maryland legislature considers it next month. He said some legislators from suburban Montgomery and Prince George's counties are "lukewarm or hostile" to the proposal. Lee added that his own support for the measure also has "cooled off."

Lee said District officials' plans to "grab a piece of our Blue Plains allocation" angered some members of his delegation. "They are saying if that is an indication of District of Columbia cooperation, to hell with them," Lee said.

The reaction by some Marylanders was not typical, however. One of the biggest challenges is to get the delegates to know that there is such a thing as a D.C. amendment.

That effort got its biggest boost last night in a single phrase, ad libbed by President Carter in his speech to the convention. After Carter got a standing ovation for his call "to wipe out discrimination based on sex and make the Equal Rithts amendment the law of the land..." the president added "and give voting rights to the people of the District of Columbia."

The D.C. delegation, led by Mayor-elect Marion Barry, Del. Walter E. Fauntroy and party chairman Robert Washington Jr., leaped to their feet and cheered the expected mention of their biggest cause here.

"That called attention to the issue like nothing we could," said Clark, who works full time on ratification for Common Cause.

The conference will be asked to approve a resolution Sunday that pledges the delegates to support ratificaton in their home states. Since the measure passed Congress last summer, only two of the 38 state legislatures needed for ratification have passed: Three others have turned it down or delayed consideration.

Barry got resolutionns adopted by the delegations of the three states assigned to him. In talks with leaders of those delegations, Barry said he was told prospects for ratification are good in South Carolina and Wisconsin, but that the Republican-controlled legislature in Indiana "will be a problem."

The president was not the only one to offer unsolicited suport for the amendment.

During a civil rights workshop, the chairman of the Democratic Party in Puerto Rico, Franklin Lopez, said residents of that territory "see a lot of parallels in the cause of blacks in D.C." and their own quest for greater participation in the federal government.

Although residents of Puerto Rico do not pay federal income taxes, as District residents do, they "pay the highest tax you can pay -- the blood tax" of fighting in American wars, Lopez said.

In hearings before several state legislatures that have considered ratification, opponents warned that if the District of Columbia gets two senators and one or two House members, all of the American territories will seek the same thing.

Frank Q. Cruz, the Democratic Chairman from Guam, said today, "We're all for D.C. getting it. It will set a precedent" that could lead to extending voting rights to his island's 100,000 American citizens.