Two members of a congressional subcommittee made an indirect but clear threat yesterday to block the Potomac Electric Power Co. from collecting $2.6 million in overdue street lighting bills owed by the District of Columbia.

Rep. William H. Natcher (D-Ky.), chairman of the House D.C. Appropriations Subcommittee, and Rep. Adam P. Benjamin (D-Ind.), a subcommittee member, insisted that Congress meant what it said when it limited the city to paying 2 cents a kilowatt hour to Pepco for street lighting.

Without an appropriation from Congress, the city would have no money available to pay the $2.6 million bill.

Natcher raised the issue at a hearing on the city budget for the 1979 fiscal year following a D.C. Superior Court ruling that the city should pay the money to Pepco. The city has not decided whether it will appeal the case.

In the ruling, Judge Joseph M. Hannon concluded that "Congress did not intend that its 2 cents a kilowatt hour spending limitation" should override the rate-setting powers of the D.C. Public Service Commission.

The 2-cent limitation, which Congress has written into the D.C. appropriation bill each year for decades, was adequate from the 1950s until 1973, the year of the Arab Oil embargo. Starting that year, the PSC allowed Pepco to add a higher fuel adjustment charge to the city's bills.

In three years, the city ran up an overcharge of $2.6 million, but Congress never granted the money to pay it. Pepco sued to collect. Meantime, the PSC restored the 2-cent rate, spreading the higher cost of the street lighting among other Pepco customers.

Natcher said yesterday tht the 2-cent limitation "is extremely fair" in view of the fact that Pepco does not pay the D.C. government for a franchise that lets it conduct a lucrative business in the city.

Benjamin agreed. "When the COngress says it's going to be 2 cents . . . that's going to be the rate," he said.

The two lawmakers made their comment to Ruth hankins-Nesbitt, chairwoman of the PSC, who testified on the commission's budget request.

Also at yesterday's hearing, Lacy Streeter, acting general assistant to the mayor, and two City Council members, Marion Barry (D-At Large) and Polly Shackleton (D-Ward 3) asked the subcommittee to approve the full $1 million being sought to pay for running the city's 36 advisory neighborhood commissions next year.

Barry and Shackleton appeared, they said, to avoid a repetition of last year's experience in which lukewarm testimony led the House to eliminate all funds for the ANCS. House and Senate conferees later approved a compromise $500,000 payment.

"My own experience with the ANC's has been . . . superb. They do an outstanding job," Shackleton said.

During the discussion Rep. Clair W. Burgener (R-Calif.) said (my phone has been ringing off the hook" since his direct complaint to Mayor Walter E. Washington got an immediate cleanup of a junk-strewn lot on Calvert Street NW. "Everyone wants me to get their alley cleaned," Burgener said. He gave the phone messages to Streeter.