Mandel administration supporters today beat back two efforts to move the site of a proposed new state prison in Baltimore. Their action resulted in the start of what is expected to be a short-lived filibuster.

Meanwhile, the House of Delegates passed a bill that would grant Prince George's County broad new permanent taxing powers. Although County Executive Winfield M. Kelly Jr. warned last week that his 1977-1978 budget depends on $5.2 million from the new tax, 13 of the county's 24 delegates did not vote for it. The measure now goes to the Senate, where its future is uncertain.

The Senate filibuster began after a majority of the Senate turned down two proposals by Sen. Robert L. Douglass (D-Baltimore) to allow the city of Baltimore to choose a site other than an abandoned Continental Can. Co. factory for a 890-inmate prison.

The 25-acre can factory site in East Baltimore sits squarely in the middle of two communities represented by Douglass and Sen. Joseph S. Bovegna (D-Baltimore). The two legislators have argued since the site was proposed that location of a prison there would destroy the communities.

"You don't understand the concern, you don't understand what's really happening, because you're so far from the situation," Douglass told the Senate. "It's a Baltimore City problem, let us decide in Baltimore City where that facility's going to go."

Douglass's amendments were opposed by most of the Mandel forces in the Senate, including fellow Baltimore Democrat Sen. Harry McGuirk.

"It's going to be similar to a second Civil War in the city of Baltimore" if the city has responsibility for choosing a prison site, McGuirk said. "I don't think it's a city responsibility; I think it should be resolved here."

The Continental Can land now is owned by politically influential developer Morton Sarubin, a cousin of Mandel's political and financial patron Irvin Kovens, who also is a codefendant in Mandel's political corruption trial.

Sarubin purchased the land last August for $1.9 million, then entered a contract with the state four months later guaranteeing him a profit of between $1.1 million and $2.6 million.

One amendment that was approved today would limit Sarubin's potential profit on the prison deal to $1.1 million. By limiting the developer's profit, the amendment eliminated some of the opposition to the sale that was based on the profit potential.

"I can go for it" with the new limit, said Sen. Charles W. Gilchrist (D-Montgomery).

After the profit amendment passed, Douglass offered another one for the purpose of beginning his filibuster. "I didn't want to take up your time, but I think this matter is of such great importance that I have to take your time," he said. "The people's interests have not been served in this matter."

The filibuster was almost averted in Senate action on Saturday. Then, Douglass lost by one vote in an attempt to remove the $26 million for the prison out of the budget when one of his supporters was out of his seat during the voting. Minutes later, Douglass lost a vote that could have led to a reconsideration of the first vote when another senator, sitting at her seat, failed to move her voting button in time to be recorded.

The split in the Prince George's House delegation in the vote on the local tax measure came, as one delegate put it, because "it's the kind of issue we've all taken public stands on. We couldn't be hypocrites." The delegation usually votes unanimously on bills suffering their county.

The bill would give the county "omnibus" or "home rule" taxing power broad enough to authorize the County Council to impose levies on telephone bills or apartment rents. Prince George's is one of the few Maryland counties that has a home rule charter but lacks such taxing authority.

At issue in the delegation were budget disputes between it and the county government.

"It's the thid year in a row that Kelly had come up and asked us for taxes to make up a huge deficit and it's the third year in a row that the deficit disappeared," said Del. Kay G. Beinen (D-Prince George's).

Despite dire warnings from Kelly about the county's financial future, the budget he proposed last week to the County Council calls for no increase in the real estate property tax.

When the "omnibus" bill came up for a vote on the House floor today, there was only an echo of the controversy: Del. Charles S. Blumenthal, another member of the county's all-Democratic delegation, asked the House to witness the split in the delegation as the vote was recorded.

Prince George's delegation chairman Frederick C. Rummage, jumped to his feet and said: "The delegation isn't divided. We deliberate and we vote differently, but the delegation is united."

Opponents of the bill see it was symptomatic of the "Band-Aid approach" to taxing.

"No matter what the tax is, I don not vote for these Band-Aid approaches," declared Del. Robert S. Redding (D-Prince George's). "We should be voting for true tax reform, not bills like this."

In previous years, the bandage applied to the county budget came in the form of an apartment rent tax that proved unpopular and unwieldy. That tax was approved by the delegation after hearing Kelly say there would be a severe budget deficit if he received no new taking authority. Most of the delegation now views the rental tax as a political mistake.

Recalling Kelly's prediction earlier this year that he would have to raise the property tax rate by 26 cents if he failed to get new taxing authority, Reddingsaid he was "very surprised at Kelly's budget." That document called for no property tax increase and provided only $5.2 million in new revenue to be raised through the "omnibus" tax.

"On at least four occasions we heard a very different story . . . credibility has to be questioned when you get the heavy doomsday treatment three years in a row," Redding said.

Among measures sent to the governor for his signature today were ones that would:

Increase state aid to community colleges by $5.7 million.

Give an additional $1 million to public libraries.

Require druggists to offer lower-cost generic drugs unless the physician insisted on a brand-name product.

Strengthen controls over strip mining.

Permit hunting of antlerless deer.

Permit the making of a home-brewed beer.