The end of a week-long filibuster over legislative reapportionment in the Maryland Senate has signaled the final defusing of what many legislators had predicted would be the most politically explosive issue of the General Assembly session.

Senate President James Clark, the Democratic leader from Howard County whose efforts to amend the plan led to the tame filibuster, resigned himself to defeat last night--virtually assuring that Gov. Harry Hughes' plan for legislative reppportionment will go into effect by its deadline on Friday..

"What was the use of going further?" Clark said as he told Senate leaders he was giving up his effort to change the governor's proposal.

Members of the House of Delegates, who already had approved a carbon copy of the governor's plan, breathed a sigh of relief after learning of Clark's decision.

"Legislative reapportionment has not been the type of issue we expected it to be," House Speaker Benjamin L. Cardin (D-Baltimore) said today. "There was only one major problem, the one in Howard County."

The gentlemanly filibuster, which began eight days ago and never lasted past 11 o'clock on any night, was the work of Prince George's County senators who were trying to avoid a vote on Clark's proposal to put the whole town of Columbia in one legislative district. Hughes split Columbia into two districts to enable the Prince George's delegation to retain its present level of representation in the legislature.

Although at the outset Clark appeared to have enough votes to win passage of his amendment, his Senate colleagues were reluctant to help him break the filibuster. When a vote to end the filibuster finally came yesterday, Clark, although expecting to lose, was stunned that only 10 of the Senate's 47 members supported him. He said he expected to have 15 votes on his side.

Some senators were clearly annoyed that Clark had persisted in a battle that would have benefited only his district, or that he would allow the speech-making to continue for days when it seemed clear his cause was lost. "I don't think Jim Clark is going to be back as president of the Senate again," one Republican senator predicted angrily.

Sen. Thomas V. Mike Miller Jr. (D-Prince George's) criticized Clark in the last hours of the filibuster and accused him of disrupting the legislative session.

But others said the Senate president had been slighted by the governor and had to fight to save face with his angry and vocal constituents in Columbia.

While the fight over legislative reapportionment may be over, a new battle has begun to develop over the governor's plan for congressional redistricting. In general the legislators are less concerned with congressional lines than with the boundaries in their own districts, but some harbor higher aspirations of running for Congress and want to use this opportunity to bolster their chances.

There is little controversy here over the changes proposed for the districts that comprise Montgomery and Prince George's counties.

Rep. Michael Barnes, a Democrat from Montgomery, would lose the conservative western part of his Montgomery County district in exchange for more liberal, Democratic territory in Takoma Park that now lies in the district of Democratic Rep. Steny Hoyer of Prince George's County.

Under the governor's plan, Hoyer's district would extend farther south to include Upper Marlboro, parts of Clinton, Temple Hills and Hillcrest Heights. Hoyer's own house, which is four blocks south of the current district line, would be included in his new district.

Rep. Marjorie S. Holt, a Republican, now has most of those areas. She would retain only the less populous south and southeastern portions of Prince George's County, including Andrews Air Force Base.