On Jan. 20, Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) put Patrick Baskette on the committee payroll as a $40,000-a-year staff assistant.

Baskette, who had been executive director of the Tennessee Democratic Party, was known to political reporters in a different role: southern regional coordinator for Biden's emerging 1988 presidential campaign. Biden aides said Baskette spent two months studying whether Biden could run for president while still running the Judiciary Committee, then moved to his campaign payroll in late March.

Joseph A. Cari Jr. of Chicago, general counsel of the Illinois Democratic Party, ended up on a different Senate payroll, that of the Senate Narcotics Caucus. Biden arranged for Cari, who will chair his presidential campaign in Illinois, to be paid $13,000 over a 15-week period. According to Cari, the $13,000 was paid for a 54-page memo on crime legislation that he wrote for Biden.

Members of Congress are always running for reelection, and their staffs are part of that process. Most officials have at least some staff members who deal with politics as well as legislation, and the two roles often prove inseparable. It is a gray area governed by an equally fuzzy set of Senate and House rules, which require that congressional aides put in a full week on official business and do campaign work only in their "free time."

"I think we were very scrupulous in keeping things separate," said Mark H. Gitenstein, Biden's Judiciary Committee chief counsel. "When this became a campaign {in March}, I insisted that anybody who remotely looked political get off the Judiciary Committee payroll. We did more than we were required."

Some of those who have worked for elected officials who remain in office while seeking the presidency make no bones about the advantages. William Dixon, who managed Gary Hart's presidential bid after Hart left the Senate last year, said, "I valued the Senate office at $2 million for a presidential campaign. One million in salaries and one million in equipment, WATS lines, word processors and desks.

"Everyone in the office is working on the campaign to a greater or lesser extent," Dixon said. "You follow the lead of the boss, and the boss wants to be president."

In Biden's case, a review of Senate and Federal Election Commission records shows that 10 people now working for his presidential campaign -- including the top three figures -- were earlier on Senate payrolls controlled by Biden, some for relatively brief periods.

Biden's is the clearest example of the value of incumbency, but there have been varying degrees of overlap among the other members of Congress seeking the presidency. Thirteen aides to Sen. Paul Simon (D-Ill.) recently went on part-time salaries in Simon's Senate offices and began taking partial salaries from Simon's presidential campaign. Most of them are lower-level clerical aides, with only two senior officials earning more than $30,000.

One is Simon's campaign manager, former representative Floyd Fithian, who had been earning $62,000 as Simon's Senate chief of staff. He now draws a $20,000 Senate salary and about $40,000 from the campaign.

Biden, who has repeatedly criticized the Reagan administration's ethical standards, declined to be interviewed for this article. His aides said they see nothing improper in the use of his Senate staff.

As early as the spring of 1986, Biden had assembled a group of political advisers, eagerly accepted speaking invitations from around the country and courted the national news media as he tested the waters for a presidential bid.

Despite this constant political activity, campaign manager Tim Ridley said Biden did not firmly decide to run until late February and was not officially a candidate until he filed documents with the FEC on March 3. Until that date, Ridley said, there was no campaign that could employ people.

But knowledgeable sources said that a number of political operatives were "squirreled away" on Biden's Senate or Judiciary Committee payroll in the expectation that Biden would run. The sources said this was done mainly in the early months of this year, when Biden's undeclared campaign had no Washington office and only a handful of paid staff members.

Many of these Senate staffers did little or no legislative work and helped run the undeclared campaign, with computers and mailing lists, out of the Russell Senate Office Building, the sources said. They said that even after the campaign office was opened in May, a few Biden aides continued to do substantial political work out of Senate offices.

Biden campaign counsel William C. Oldaker warned the senator's staff in a June 2 memo that it is "important to avoid even the appearance of impropriety," and that any Senate aide who is "substantially involved" with the campaign should take a salary cut or leave of absence. Failure to do so, he said, "could lead to questions by opponents and the press regarding the appearance of improper use of Senate staff."

Ridley was hired last October as the senator's $64,000-a-year administrative assistant, but he was widely known to staff and reporters as Biden's campaign manager. Ridley formally assumed that title and moved to the campaign payroll April 16.

Ridley said he spent considerable time on Senate budget and personnel matters before April 16, but that this was hard to separate from the emerging campaign.

"I ran the {Biden} Senate office," Ridley said. "I advised him through the whole process of whether it was actually feasible to juggle being a member, being chairman of the Judiciary Committee and running for national office . . . . I worked probably 100 hours a week, literally."

Michael E. Cryor was given a $40,000-a-year job in Biden's personal Senate office March 24. His political experience included managing the unsuccessful 1986 Senate primary campaign of then-Rep. Michael D. Barnes (D-Md.). Cryor became Biden's deputy campaign manager June 1.

Ridley said Cryor, a former House aide, was hired to handle banking and urban issues and that it was not decided until later that he would join the campaign. But sources said that Cryor was introduced to Biden's staff as the deputy campaign manager and that one of his first tasks was to negotiate a lease for the campaign's office space.

Ridley, Cryor and others "were doing nothing but pure, unadulterated campaign politics," one source close to the campaign said. "We didn't hire these people to do anything but the campaign. They never made any pretense that they were doing Senate business."

Biden's campaign committee reported raising $1.7 million for the period ending March 31, more than any other Democratic candidate. But the campaign paid only token salaries to a half-dozen aides in March. The largest amount, $2,168, went to campaign treasurer Ted Kaufman, Biden's $60,000-a-year Senate chief of staff -- who held the title of administrative assistant for many years until it was given to Ridley in January. Kaufman drew half his Senate salary during March before joining the campaign full time April 1.

Ridley said his job in March and early April was "preparing the Senate office for my transition to the campaign." The campaign was launched during this period, absent a Washington office until one was opened in early May at a cost of $3,500 a month.

The Biden campaign -- so frugal that aides have been sent home to Washington from late-night Delaware meetings to avoid hotel bills -- may have been trying to cut costs by having employes stay on the Senate payroll as long as possible. And some Senate aides may have delayed joining the 70-person campaign because they have had to take major pay cuts.

Cari, a partner in a Chicago law firm, was put on the Senate payroll during a period when he says he was commuting here about once a week, lining up political support for Biden in Illinois and setting up dinners with House members in Washington.

Neither Cari nor Biden aides could say how many hours Cari worked for the Senate or how his compensation was determined.

Cari was paid $13,039 from Oct. 1 to March 10 by the Senate Narcotics Caucus, which Biden cochaired. He was then placed on the Judiciary payroll for two days and paid another $200. Biden aides said they felt he deserved more money.

"We just agreed on an amount of money to pay him," Gitenstein said. "Sometimes we paid him a little more for travel. We basically ended up picking up his air travel."

Cari said he is "very proud" of the memo he wrote for Biden, which analyzes recent narcotics and money-laundering legislation. He noted that he has served on an oversight board for the Cook County prosecutor's office.

"Doing public service appeals to me," Cari said. "The compensation part of it to me was fairly secondary."

Baskette, Biden's southern coordinator, was paid $6,222 by the Judiciary Committee from Jan. 20 to March 15, and joined the campaign the next day. Three days before he went off the Senate payroll, the Biden campaign gave him $2,000 for travel expenses.

Ridley said that Baskette and a young aide, Nathan Siegel, were hired by Judiciary to pore over Biden's schedule and decide whether he could run for president without neglecting committee duties.

Siegel was placed in an $18,000 job in Biden's personal office in December, then moved to Judiciary until March 19. The day he went off the payroll, Biden's campaign gave Siegel $597 for travel expenses and sent him to Iowa for six weeks of political organizing.

Siegel has now been rehired by Biden's personal office, where aides say he is working on position papers. Some are reviews of Biden's accomplishments, which aides concede will be useful to the campaign.

Gitenstein, the Judiciary Committee's $70,000-a-year chief counsel, has also been increasingly active in issues development for the campaign. Senate sources said Gitenstein spends little time on committee business, but Gitenstein said he has delegated day-to-day management to a deputy.

"I have been spending more time writing speeches for Joe . . . . but I've always averaged 40 hours a week on Judiciary," he said. "I might spend six hours working on a major speech, but the weekend before I would have spent the whole weekend on Judiciary."

Gitenstein said that numerous aides were moved from Biden's office to Judiciary because the committee budget contains "a huge amount of money" and was running a surplus.

"You have to turn money back at the end of the fiscal year, so you try to spend as much of it as you can," Gitenstein said.

Questions have been raised about other Biden aides, whose work campaign officials defended as involving the normal overlap between legislative and political functions:Ruth H. Berry, who travels with Biden on the road, was put on the Judiciary payroll in a $52,000 job for two weeks in March, then shifted to Biden's Senate office. While Berry was still on the Judiciary payroll, the campaign began giving her payments for travel expenses. Biden aides said every senator needs a traveling aide to stay in touch with Senate business.

Since April 16, Berry and three clerical aides have received part-time salaries from the campaign and Biden's Senate office. Fariborz Fatemi had been Biden's traveling aide while holding a $56,000 Judiciary Committee job. He was switched to Biden's personal office March 26. Sources said Fatemi, who was paid $942 for campaign travel in March, now concentrates on the Democratic National Committee for Biden.

Oldaker described Fatemi as Biden's "political director" and liaison to organized labor. "In almost every Senate office they have someone to talk to political constituencies," he said. Albert A. diClemente, the $61,000-a-year director of Biden's Wilmington Senate office, said he has made a half-dozen political forays to Iowa and New Hampshire, but only during weekends or vacation time. (Congressional staffers may take as much vacation time as their boss allows.)

"I don't think Joe is doing anything different than anybody else," Oldaker said.

A Congressional Research Service summary of Senate and House rules says that "a staff employe may engage in campaign activities . . . during the staffer's 'free time' or 'off-duty' hours as long as the employe does not neglect the official congressional duties for which he is receiving compensation from public funds."

But there are "no specific job descriptions" for congressional staff members and "no detailing of what a staffer's 'official' duties may entail."

On the Simon campaign, spokesman David Carle, one of the 13 aides whose salary and time is split between the Senate and Simon's campaign, said, "No one is financially benefiting by this arrangement. It was just the right thing to do."

Campaign manager Fithian "is still overseeing the Senate office; he's clearly putting in enough hours," Carle said. One aide from Simon's Senate Labor subcommittee is splitting her time, while subcommittee counsel Ira M. Lechner has resigned to be Simon's labor coordinator.

"This is a subject that most campaigns struggle with because it is loose," said Don Foley, press secretary for Rep. Richard A. Gephardt (D-Mo.), who splits his salary between Gephardt's House office and presidential campaign. He said one other Gephardt aide has joined the campaign.

Senate Minority Leader Robert J. Dole (R-Kan.) controls a large Senate staff. But only his administrative assistant, Mike Pettit, and a receptionist have joined his presidential campaign. Three House aides to Rep. Jack Kemp (R-N.Y.), including spokesman John Buckley, have joined his campaign.

Seven aides to Sen. Albert Gore Jr. (D-Tenn.) will join his presidential effort July 1, but press secretary Michael Kopp said he and other top Gore aides are taking vacation time this month while working for the campaign.

Eight high-level aides to Massachusetts Gov. Michael S. Dukakis (D) have joined his presidential campaign, including chief of staff John Sasso and the deputy chief of staff, personnel director, chief counsel and unemployment commissioner.

Sasso, now campaign manager, said he and other top aides went on the campaign payroll April 1, the day the campaign committee was formed and two weeks after Dukakis announced his candidacy. Sasso acknowledged that part of his state job was inherently political but said that before Dukakis' announcement, "The governor was very clear with us -- he didn't want us doing any national politics until after he made a decision."

Detailed records for the Simon, Gore and Dukakis campaigns were not available since they were formed after the FEC's most recent filing deadline, March 31.

Other prospective candidates have used another vehicle to finance their pre-presidential campaigns.

Dole, Kemp and Vice President Bush set up "multicandidate" political action committees (PACs) -- which are designed to make donations to other candidates -- and used most of the money raised to pay for Washington offices, extensive political staffs and travel to key states.

Biden's PAC, Fund for '86, spent all of the $133,000 it raised in donations, allocating only small amounts for travel by a few aides. Biden has a third campaign fund, for his 1990 Senate reelection, which has a $420,000 surplus.