President Reagan, who has opposed increased funding for public broadcasting in the past, yesterday vetoed a Corporation for Public Broadcasting authorization bill that would have provided public TV and radio $238 million in fiscal 1987, $253 million in fiscal 1988 and $270 million in fiscal 1989.

The veto was announced in a White House statement. In his message to the Senate regarding the veto, President Reagan said the issue was one of "long-range fiscal prudence."

"Public broadcasting," he said, "constitutes an important national resource and contributes to the diversity of news, information and entertainment choices available to the American public. Under S. 2436, however, federal funding for public broadcasting would be increased by too much too fast."

White House spokesman Larry Speakes said Reagan was committed to public broadcasting and would support an increase in funds -- "just not as high as in this bill."

Reagan's action was the first presidential veto of a CPB authorization since President Nixon rejected a two-year authorization in June 1972.

In that instance, Congress resubmitted within 48 hours a one-year authorization bill that the White House permitted to stand.

Public broadcasters were shocked by yesterday's veto.

The Reagan administration had recommended $100 million in spending authority in 1987, $85 million in 1988 and $70 million in 1989.

But most broadcasters had chosen to ignore that warning signal because of the level of support they enjoyed in Congress this session, particularly from Reps. John Dingell (D-Mich.) and Timothy Wirth (D-Colo.) and Sen. Barry Goldwater (R-Ariz.), support the president clearly read another way.

None of the public broadcasting executives contacted yesterday harbored hopes for a congressional override of the veto, but all vowed to renew the battle for increased funding.

Spending levels for public TV and radio had been on hold since 1981, but intense lobbying this year had seemed to produce a turnaround for the industry.

The veto will have no immediate effect on public broadcasting. The bill would have extended the authority of CPB to receive federal funds, but was not an appropriation measure. Actual funds must be approved by Congress in separate legislation.

Nonetheless, Wirth, chairman of the House subcommittee on telecommunications, consumer protection and finance, a leader in this year's fight for more public broadcasting funds, yesterday called the veto "an absolute outrage and a brutal slap in the face to the nation's children and another assault on millions of moderate- and low-income Americans that, but for public broadcasting, would not have access to a wide range of cultural events and educational programs."

However, Rep. James T. Broyhill (R-N.C.), ranking Republican on the full House Energy and Commerce Committee, said in a statement: "I think the president made a prudent decision in rejecting the huge increase called for in this legislation. I personally support a modest 15 percent increase in funding for public broadcasting, but the overnight 49 percent increase outlined in this authorization bill just goes too far, too fast. Especially since individual and corporate donations to public broadcasting during the past 12 months were at record levels."

Edward J. Pfister, president of CPB, said in a statement that "we have all sustained a serious setback. But there is also no question that we shall begin again -- right now, to overcome this setback and to win adequate federal funding for public broadcasting in this nation."

CPB board chairman Sharon Percy Rockefeller said the veto "represents a real loss for 200 million Americans who depend on public television and radio for education and information. It's a particular loss for children's programming."

"It's a terrible shame," said Bruce Christensen, president of the Public Broadcasting Service. "The bill represented years of analysis and help from all sectors -- commercial broadcasters, the Congress, the industry and our constituency. Now, our long-term stability, our program-planning capacity, all get undercut. The local stations can't make plans into the next decade and that's a very serious aspect."

Peter Fannon, acting president of the National Association of Public Television Stations, the PBS lobbying arm, called the president's action "extremely depressing. It threatens considerable turmoil in the industry". . . Also in the News

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Penny Mickelbury, who has been acting news director since Goldberg's departure, will continue as assistant news director when Ostrowski joins the station. . .

Before moving to Cleveland, Ostrowski was corporate director of news for the Post Co. of Appleton, Wis., and served as news director for two of that firm's stations, WLUK in Green Bay, Wis., and WOKR in Rochester, N.Y. . .

"Good Morning America" will air a tribute to Doug Benefield, the chief test pilot for Rockwell International, who was killed in yesterday's crash of a B1 prototype bomber in California's Mojave Desert. . .

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Steve Sohmer, one of the rising executives at NBC, rose a little higher yesterday when he was named executive vice president of NBC Entertainment. . .

With the promotion, Sohmer added "The Tonight Show" to his list of network responsibilities, which already includes advertising and promotion, daytime, Saturday morning (children's programming) and specials. . .

Sohmer, who will continue to report to NBC Entertainment president Brandon Tartikoff, will also add divisional administrative duties to his extensive re'sume'. . .

Sohmer joined NBC from CBS in July 1982 and quickly established himself as a comer. . .

NBC's Saturday morning lineup is now No. 1 among the three networks and even its daytime schedule, although still ranked behind CBS and ABC, is getting a larger share of the audience every week since he took over that department. . .

Talk about your Giants: ABC's "20/20" will feature a Barbara Walters interview with CBS' Mike Wallace, quintessential questioner for "60 Minutes" on a show scheduled for late September. . .

Are you just imagining that NBC is filling the air with promotions for the upcoming "Miss America Pageant" the night of Sept. 15th?. . .

A spokesman for NBC said yesterday that actually, the number of on-air promos for the pageant will be about 90 this year, "maybe a little more," but that NBC aired 90 last year, too. . .

The 10-second spots have been aired on daytime shows for the first few weeks of the annual pageant campaign because the networks reserve the prime-time spots (a total of 18 in 1981) for the last couple of weeks before the telecast. . .

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