Members of the Senate Ethics Committee had some bad news for Sen. Edward W. Brooke (R-Mass.) yesterday, predicting they would not complete their probe of alleged irregularities in Brooke's financial affairs before the Sept. 19 Massachusetts senatorial primary.

Noting that the Ethics Committee had been held up inpart because of Brooke's own efforts to limit the scope of the investigation, Sen. Harrison H. Schmitt (R-N.M.) said the committee's final report on allegations about Brooke and Sen. Herman E. Talmadge (D-Ga.) would probably not be ready before mid-October.

Schmitt's prediction, which was made to reporters after a committee review of the cases against the two senators, leaves Brooke with several unresolved allegations hanging fire at a time when he is seeking the nomination for his third Senate term. Talmadge is not up for reelection until 1980.

Brooke has admitted he "made a mistatement" about a $49,000 loan listed in his divorce papers. News accounts have also said he incorrectly listed his daughters as dependents on his tax returns and that he failed to disclose his interest in a Washington cooperative apartment in his Senate financial disclosure. Brooke has denied any wrongdoing.

A spokesman for Brooke said yesterday that he did not believe the Senate committee's probe will have any effect on Brooke's primary campaign.

The Ethics Committee and a federal grand jury here are both investigating allegations against Talmadge. The Ethics Committee chairman, Sen. Adlai E. Stevenson (D-Ill.), said his committee will get bank records today concerning $13,000 in improper Senate reimbursements which a former Talmadge chief aide has said were sought on Talmadge's orders.

Talmadge is scheduled to be questioned sometime before next Wednesday. Carl Eardley, special counsel for the committee, declined to reveal when or where he would question the Georgia senator but said it would not require Talmadge to talk under oath.

Stevenson also said the committee had reached no decision yesterday about how much interest Talmadge will have to pay on $37,125 he repaid the Senate earlier this week for improper expense claims.

Meanwhile, the Massachusetts attorney general's office announced yesterday it was investigating additional news reports that Brooke's late mother-in-law received Medicaid funds in violation of state and federal guidelines.