Walter Weikers and Charles Edward Neiswender, charged with separate attempts at obstructing justice in the aborted political corruption trial of Gov. Marvin Mandel and four codefendants last month, pleaded innocent in arrangements here today.

Responding to a request from chief prosecutor Barnet D. Skolnik that the suspects be given a speedy trial, U.S. District Court Judge Frank A. C. Kauffman set tentative trial dates for later this month for both Weikers and Neiswender.

Skolnik asked the judge to release Neiswender on personal recognizance, a move that added to speculation that the self-styled "con man" is cooperating with prosecutors in their investigation.

Both Neiswender, 51, of Cinna minson, N.J., and Weikers, a 67-year-old Pikesville furniture salesman, are thought to have acted as middlemen for an individual whom prosecutors have called "the shark," who allegedly hired the two to disrupt the trial.

Weikers, who mortgaged his house in suburban Baltimore to post the $100,000 bond last month, is not believed to be cooperating. His attorney, Harold Glaser, sought to have the trial postponed until May, but Skilnik said that "in the interest of justice," both men should be tried "at the earliest possible dates." The prosecutor said they are "very simple cases" and could be disposed of in two days of trial.

It is believed that the prosecutors hoped to dispose of jury tampering charges before the second trial of the governor and his codefedants begins. A hearing is scheduled here next week to discuss a date for the second trial.

Kauffman set Jan. 17 as a tentative date for Weikers' trial, but also set March 14 as an alternate date. For Neiswender, the judge set an early date of Jan. 31 and an alternate of Feb. 28.

Neiwender was arrested Nov. 5, more than a month after he allegedly contacted Mandel's chief attorney with an offer to disrupt the trial. Weikers was arrested Nov. 30 after he allegedly offered $10,000 to juror Oscar Sislen, a relative by marriage to press for a not guilty verdict or a hung jury's deliberations.