A government psychiatrist testified yesterday that she probably was the first woman with whom John W. Hinckley Jr. had ever discussed deeply personal matters.

She disputed a defense lawyer's suggestion that Hinckley played down his mental problems in interviews with her in order to win her friendship.

Psychiatrist Sally A.C. Johnson, who has told the jury at Hinckley's trial that he was in control of his behavior when he shot President Reagan, testified yesterday that Hinckley was generally "honest and open" during 55 interviews with her.

Johnson, a key prosecution witness who first talked with Hinckley four days after he shot the president and three others and interviewed him more times than any other psychiatrist, told the jury yesterday that she believes Hinckley did withhold some information from her.

After several months of thinking about criminal responsibility -- the key issue in his trial -- Hinckley didn't tell her about other crimes he considered before he shot Reagan because he did not want to present himself as capable of planning, Johnson testified.

Johnson, a staff psychiatrist at the U.S. prison in Butner, N.C., where Hinckley was held after the March 30, 1981, shooting outside the Washington Hilton Hotel, said Hinckley was suspicious of her because she worked for the government.

That suspicion left, she said, after she informed him she was conducting an independent mental evaluation at the direction of the court.

"I think John did want me to like him as a person," Johnson testified.

"Isn't it true that he did not want to appear bizarre or irrational or unstable or in any way crazy with you?" defense lawyer Gregory B. Craig asked Johnson during a full day of cross-examination.

"I certainly don't think that's the case . . . I think John was trying to give me an honest picture of how he was," Johnson responded.

Johnson, 29, was several months pregnant during the four-month period that she talked with Hinckley.

When she asked to see some of Hinckley's prolific writings, she said, he composed a poem for her entitled "A Poem for my Favorite Pregnant Psychiatrist."

In the poem, introduced into evidence yesterday, Hinckley wrote about going to a beach to eat hamburgers, watch mermaids "flopping their fins" and collect sea shells.

"This dangerous movie is finally over," Hinckley wrote in the final stanza, "so let's leave the darkness and go find fresh air."

Defense lawyer Craig suggested in his questioning that Hinckley wanted to be seen as someone that Johnson could be fond of and that the poem showed his desire to have a relationship with her beyond doctor and patient.

Johnson said that she believed the poem merely reflected Hinckley's desire for outside contacts other than long interviews with doctors and lawyers involved with his case.

Johnson also testified that while Hinckley fantasized about actress Jodie Foster, whom he had pursued with letters, poems and telephone calls, he always knew he would never have a personal relatinship with her.

According to Johnson's interview records, Hinckley said he wanted to write to Foster and ask her "to stop keeping her distance from him" and he once suggested that it would be good therapy for both him and Foster if they corresponded.

Johnson said Hinckley had a "realistic expectation" that Foster would react to his statement that he shot Reagan to gain her attention, and that he was slightly disappointed when she made no response.

In her testimony yesterday, Johnson also acknowledged that Hinckley claimed in interviews with her that he had written to Foster about stalking former President Carter -- letters Foster said she never received.

This angered Hinckley, who accused the actress of feigning ignorance, sought to ask her why she was playing "Little Miss Innocent" and then went on a hunger strike -- not because he thought he had a relationship with Foster, Johnson testified, but in protest of his lawyer's refusal to allow him to contact Foster.

There has been no evidence at the trial that the letters mentioned by Hinckley were written, mailed or received by Foster.

In another development yesterday, Judge Barrington D. Parker said he wanted to know by today whether the defense plans to present any additional evidence, including testimony by Hinckley, after the government experts have finished their testimony.

Three defense psychiatrists already have testified that they believe Hinckley was legally insane when he shot Reagan.