Sen. Thomas F. Eagleton (D-Mo.) stepped up his attack on Donald J. Devine yesterday, suggesting he was not qualified to be reappointed head of the nation's civil service system because he improperly mixed Republican political campaign activities with his official duties.

Devine, facing hours of close questioning by Eagleton and Sens. Carl Levin (D-Mich.) and Albert Gore Jr. (D-Tenn.), said his activities were proper because he did not bill the government for political travel and because the director of the Office of Personnel Management (OPM) is not covered by the Hatch Act, which bars civil servants from participating in partisan politics.

"The taxpayers can be absolutely certain, since I work 12 to 13 hours a day, often on weekends, that they get much more than 40 hours a week from me . . . ," Devine said on the second day of confirmation hearings before the Senate Governmental Affairs subcommittee on civil service. "A presidential appointee works 24 hours a day, 365 days a year."

Devine, who was an official of the 1980 Reagan-Bush campaign, made dozens of appearances on behalf of at least 12 Republican congressional candidates in six states last fall, according to testimony yesterday.

In most cases, he was accompanied by his top OPM aides, who are also former Reagan campaign officials. Devine said he needed the staff to come along to help keep in touch with the agency and to conduct official business while he travelled.

Eagleton cited a 1984 Devine campaign appearance in California on behalf of Republican State Assembly candidate David Schell, who was running against Democrat Tom Hayden.

"Schell reimbursed you $69 and Uncle Sam paid the rest . . . ," Eagleton said. "It was sure a bargain for the Schell campaign: $69 for a presidential appointee."

Devine said he traveled to Los Angeles on official OPM business, which included meetings and a speech. His political appearance, he said, was a side trip. "There are very precise rules for this, and we follow them meticulously."

A vote on the reappointment of Devine to another four-year term is expected this afternoon. Senate Democratic staff members said they were hopeful they could sway at least one of the full committee's seven Republicans to join the panel's six Democrats in blocking Devine's nomination.

But Patrick Korten, an aide to Devine, said Devine is "very optimistic" he will be reconfirmed. "This is just hazing. This is hell week . . . . We'll get through."

At one point, Levin told Devine, "You have been very openly partisan and political in the way you have run this office. You have been out blasting congressmen, telling people in districts that they have bad congressmen."

But Sen. Ted Stevens (R-Alaska), the subcommittee's chairman, disputed that, saying that Devine's campaign work did not intrude on his management of OPM.

Gore also faulted Devine for allowing the federal employe health benefit program to build up a "bloated" reserve approaching $2 billion, or 30 percent of annual premium revenues.

Gore said that federal and private actuaries had said that a reserve of between 5 and 10 percent was adequate, and that the excessive reserve contributed to high premiums and low benefits for federal workers.

Devine acknowledged after questioning that he plans to reduce the reserve to about 16 percent, which he said could reduce premiums.

Eagleton also said he believed that Devine was not telling the truth when he denied that he had arranged to let OPM's his made a political deal to allow his associate director, George Nesterczuk, to leave the agency OPM to run a GOP Republican political campaign and then return on the Monday following the 1982 election.

Nesterczuk, a friend of Devine's who ran Lawrence J. Hogan's Maryland Senate campaign for a Senate seat from Maryland that year, left OPM for nine weeks. Asked whether he had guaranteed that Nesterczuk could have his job back if Hogan lost, his friend a job in case Hogan lost, Devine said, "I did not leave his job open, but I did not fill it."