A probate Court judge decided yesterday to allow a new divorce trial for Sen. Edward W. Brooke (R-Mass.) if his wife, Remigia, requests one. Immediately after the judge's decision was announced, the Middlesex County district attorney said he will decide today whether to prosecute the senator on perjury charges for lying under oath during the initial divorce proceedings.

District Attorney John Droney, who ran against Brooke for the Senate in 1972, declined further comment on the court order issued yesterday, the day the Brooke divorce was set to take effect. However, he has said his options on the senator's case include criminal prosecution.

Mrs. Brooke, who was given 10 days to decide whether she wants a new trial, will meet with her attorney, George Ford, to discuss the case this morning, Ford said. The judge said in the ruling that he thought a new trial might not result in a larger settlement for Mrs. Brooke.

In his 12 page decision on last week's preliminary hearing reopening the divorce case. Judge Lawrence T. Perera said that Brooke's financial statements given in a May 12, 1977, deposition were "false and could reasonably have misled" Mrs. Brooke about the senator's financial condition.

The judge ruled that the divorce settlement was "fair and equitable" but that Brooke "did not make a true and complete disclosure" of his financial condition.

Brooke, who is running for election to a third six-year term, testified last week and has said in a press conference that he "made a misstatement" about a $49,000 loan.

On the deposition he stated the loan was from a friend, liquor distributor A. Raymond Tye. Later, Brooke said only $2,000 was from Tye and the rest was from his mother-in-law. His wife's lawyers have attempted to prove that this altered his net worth.

The Senate Ethics Committee has opened an investigation into Brooke's finances because he failed to claim the loan on his Senate financial disclosure. He also faces an audit from the state tax department.

Brooke testified he lied about the loan because he did not want to "bring out the family matter."

The judge ruled the mother-in-law's funds which were kept in Brooke's personal checking account did not constitute a personal loan despite Brooke's testimony that he felt "in my head and heart" that it was a personal obligation. The effect of this ruling was to find that Brooke was worth more money than he had said he was during the original divorce proceedings.

However, the judge declined to institute contempt proceedings, noting Brooke's "personal and professional pressures" during the divorce.

Brooke was ordered to pay all court costs during the preliminary hearing last week because, the judge said, his admission publicly that he had "lied" had sparked the court's reopening of the case.