The 38,000-member Maryland teachers' union gave an important boost to underdog gubernatorial candidate Theodore G. Venetoulis yesterday, voting him a strong endorsement. Along with it comes the organizational help of thousands of campaign volunteers as well as a possible $200,000 in campaign contributions.

Venetoulis, the Baltimore County executive and a former community college teacher, won the endorsement at an all-day convention of the Maryland State Teachers Association despite an intense lobbying drive by campaign workers and supporters of the front-runnign gubernatorial candidate, Acting Gov. Blair Lee III.

Lee so actively sought the endorsement he had his workers release a statement in which he substantially revised his stand on a pension reform proposal that was bitterly opposed by teachers at the last legislative session. Nine state legislators who support Lee were enlisted to lobby teachers from their districts at the convention.

But the energetic activity of the Lee team was not enough to offsett the strong support for Venetoulis, who has been courting the educators for more than a year by visiting nearly every local teacher group in the state and arranging breakfast meetings with union leaders. than a year by visiting nearly every local toucher group in the state and arranging breakfast meetings with union leaders.

The 44-year-old Baltimore Countian practiced his personal style of campaigning at the weekend convention, hugging and kissing teacher delegates at a breakfast reception in his hotel suite and pinning "Venetoulis for Governor" buttons on suite lapels and blouses as the educators took their seats to vote.

When the time of reckoning arrived, the teachers voted 237 to 145 to support a recommendation of their executive committee endorsing Venetoulis. The 61.7 percent of the vote cast for the couty executive was more than enough to meet the 58 percent margin required for a union endorsement.

"This is the first part of a very basis struggle in our state," Venetoulis told the teachers after jogging through the standing, applauding convention to accept the endorsement. "Let me now teach the old political machines in the state their first lesson. Never role out the people."

Venetoulis, who calls himself a reform candidate and tries to link his competition to Maryland's recent history of political corruption, said in a later interview, "If you're challenging a crowd like this (Lee), you need a group like the teachersto equalize the weight, a group like this deals directly with the people."

State Senate President Steny H. Hoyer,who filled the lieutenant governor's slot on Lee's ticket four days ago and marshaled the lobbying foray at this weekend's convention, said the Venetoulis endorsement "has got to help his campaign. Anytime you get the support of a statewide organization, it's got to help."

The endorsement substantially shores up Venetoulis' campaign at a himself by merging with Hoyer, a good campaigner who brings to the ticket a strong base in his Prince George's County and important support within the General Assembly.

"The teachers are a potent group," Fran Tracy, compaign coordinator for the Lee-Hoyer ticket, said before the vote yesterday. "Whoever gets their endorsement will add momentum to the campaign. The teachers obviously hold a position of respect in the community. Its a very important endorsement to have."

The endorsement of the teachers' union is one of the most sought after in this election year because of its large size and its plans to set up offices in each county of the state to assist favored acndidates in raising campaign funds, fielding volunteers and providing professional political consulting.

A professional political organizer was hired several months ago to show teachers how to write position papers, canvass neighborhoods, run a campaign offices and distribute campaign materials. They will be expected to work through PTAs and community associations in their own communities.

Maryland State Teachers Association President Peter V. Tribley said he hopes to raise an average of $5 from each member to pay for the costs of running local campaign offices. He said some of the contributions may be directly funneled to endorsed state and local candidates, while most of the money will be used to campaign as their behalf.

The teachers' union has endorsed state and local candidates in past elections, but the group has never before made such an ambitious political organizing effort. The new strategy is designed to enchance teachers' bargaining power before legislative bodies by becoming indispensable to the politicians who make up those bodies.

The "teachers' lobby" is one of the most effective and successful pressure groups in Annapolis, consistently getting its way with education aid formulas, teacher tenure practices, curriculum conrol and retirement benefits. In the last session, it defeated a Lee-backed proposal to reform the costly pension system.

It was Lee's support of the unpopular pension measure, according to many teachers, that made him unacceptable for endorsement despite last-minute changes in his position. "We just don't trust Blair," Jane Hardy of the Montgomery County Educators Association, told Hoyer when he tried to solicit her support.

Many political observers in Maryland and elsewhere predict a gradual transfer in power from the traditional political organizations to such well-financed and well-organized groups as the teachers' union because of their ability to field a large campaign crew as well as to raise campaign funds from their long membership rolls.

The Maryland teachers have been among the most heavily courted of those groups. In addition to Lee and Venetonlis, their endorsement was sought by other Democratic candidates for governonr: State Attorney Geneeral Francis (Bill) Burch, Baltimore City Council President Walter S. Orlinsky and former state transportation secretary Harry R. Hughes.

Burch, who is running as a conservative-populist candidate, said he knew before the convention that the delegates were committed to either Venetoulis or Lee. Instead of seeking their support with what he called "well-mannered public sympathizing" and "soft-shoe politicking," he amied his speech at a lager audience of "those who are fed up with the education system."

In return for increasing doles of taxpayers' money, he said, all the public gets is "barely rising standards of literacy, and growing numbers of functional illiterates churned out at the end of the line, unable to read a sign, write a check or pay a bill."

"The more money you get," Burch said, "it seems the worse the prognosis for our children's and the public has a right to expect from you . . . the best possible job at every level. For whatever reason, you are not giving them this. Instead you are going back to the well of public resources for more pension rights, as if that well were inexhaustible."

Burch, who barged into Hoyer's press conference last week to denounce Hoyer's merger with Lee, was largely ignored by the nearly 400 teachers milling around the convention hall.