The D.C. Council gave preliminary approval yesterday to a bill that would allow the city's police officers to work part time as private security guards in Washington and wear their uniforms at those jobs.

In a nearly four-hour session, the council also rejected an effort to lengthen the outdoor public swimming pool season, opposed a proposed moratorium on collecting private home water bills over $200, and passed a $63.8 million supplemental operating budget for the curent fiscal year.

The outside employment measure for police passed 7 to 4 on a roll-call vote after the council heard arguments that the bill would benefit police officers, many of whom live outside the city, at the expense of District residents who want jobs but cannot compete with trained police.

"We're hiring too many people who live elsewhere," said council member Jerry A. Moore Jr. (R-At Large), arguing that the city cannot tax the income of nonresidents. "We should have a responsibility to ourselves to recycle money in the District of Columbia for our own benefit."

Other council members argued that off-duty police working in uniform would deter crime and increase the security of businesses and consumers.

The Fraternal Order of Police, which represents rank-and-file officers, has strongly supported the bill. Officers in other area jurisdictions are already allowed to work in uniform at part-time jobs.

Voting for the measure were council members John A. Wilson (D-Ward 2), Betty Ann Kane (D-At Large), John Ray (D-At Large), Polly Shackleton (D-Ward 3), William R. Spaulding (D-Ward 5), David A. Clarke (D-Ward 1) and Chairman Arrington Dixon.

Opposed were Moore, Hilda Mason (Statehood-At Large), Wilhelmina J. Rolark (D-Ward 8) and Nadine P. Winter (D-Ward 6). Council members Charlene Drew Jarvis (D-Ward 4) and H. R. Crawford (D-Ward 7) were absent for the vote.

The bill is scheduled for a final vote May 4.

The council approved with only minor changes Mayor Marion Barry's proposed $63.8 million supplemental budget, including additional funds for Medicaid payments, city workers' salaries and public housing projects.

In the course of that action, the council by voice vote rejected Kane's attempt to provide $250,000 from the supplemental funds to open the city's 19 outdoor pools for three weekends beginning with Memorial Day and for an extra week at the end of summer, including Labor Day.

One council member close to the mayor said Barry will offer a similar proposal later this week, recommending spending an additional $250,000 for recreation, including funds to open the pools for the Labor Day week. Barry, who watched part of the council debate yesterday, said he would make an announcement Friday but declined to elaborate.

On water bills, Ray called for a moratorium on collection of bills over $200 for private homes, but withdrew his proposal after several members said that although their offices have received complaints about inaccurate or missing bills, they do not consider the situation an emergency.

Some members said privately that Ray's bill was seen as an attempt to embarrass the Barry administration in the wake of last week's disclosures by Ray that some citizens have received erroneous bills of more than $12,000.

The council yesterday also approved amendments to pending cable television legislation, including a proposal by Winter that the bill include a provision against obscenity as defined by the city's current laws.